First, Languedoc and Occitania (the second being partly a savant transliteration of the first) wasn't used in Middle-Ages to name the entirety of the occitan-speaking region, but at first the part of this area ruled directly by Capetian kings which had to use a brand new name because this precise region simply had no real definitive name.

You did have, nevertheless, specific terms to name a political and cultural reality in southern Gaul/France but these were really archaising past the Xth century.

The first, and probably the main one, was Aquitania.
In the Early Middle Ages, and especially after the Frankish conquest of southern Gaul on Goths, it served to name a political and cultural ensemble vaguely delimited by Loire, Cévennes and Pyrénées. With time, distinction grew more and more compared to the traditional Frankish "cores", and Aquitaine was divided among Frankish kings as sort of a "quasi-foreign" sub-realm when local nobility didn't supported (without lasting attempt, tough) having their own sub-kings (Gondovald, Caribert II, Eudon mostly). Charlemagne still had to recreate a sub-realm of Aquitaine with his son Louis as ruler.
With the shattering of Carolingia, Aquitaine ended up being a formal sub-kingdom of Western Francia without effective reality in itself, but which was referred quite a lot by local nobility willing to preserve a certain independence and critically to impose their local hegemony : as such, it's not rare to see Western Frankish kings using such titles as "King of Franks and Aquitains".

Aquitaine was pretty much shattered too, tough, and with the War of Succession of Auvergne (long story short, Guilhelmids disappear, war between Houses of Poitiers and Toulouse for leadership, ending up with Aquitaine being durably split in three blocks themselves significantly shattered). By the XIth century, then, Aquitaine was antiquated and let place to Guiana (Aquitaine is the savant evolution of Aquitania, Guiana comes from popular form Aguiana, which in english and french gives Guienne), Peiteus, Tolsan, the return of a very distinct Auvergne, etc.
Aquitaine remained a pretty much prestigious names, and Occitania owes a bit of its linguistic formation to the final -tania (basically a mix of Aquitaine and Languedoc)

Nowadays, Languedoc mostly means the part of southern France set between the coast, Rhône, Corbières and Cévennes. (which is, strictly speaking, the Lower Languedoc). Interestingly this precise region used to have specific names which fell too in desuetude in the Xth century (for pretty similar reasons).
When Franks took over southern Gaul, they let a part of this region to Goths which called it their province of Gaul**,** while Franks and Aquitains called it Gothia.
With the collapse of the Visigothic Kingdom and Carolingian takeover of the region, the latter name stuck for a bit and as what I described above, you had at least one occurrence of "Kings of Franks, Aquitains and Goths" in history (although Gothia never was considered a sub-realm). The definition was a bit blurred, tough, since regions outside former Gothia were included (Toulouse's region, the March of Spain, etc.). Initially, the Count of Toulouse were marchios (marquis) of Gothia but the title fell in disuse too around the Xth and with little posterity except maybe on the other side of Pyrénées : indeed Catalonia might come from "Gothia Lunga" (long Gothia) as Gothia was "elongated" of transpyrenean lands taken on Arabo-Berbers which eventually went on their own in the Xth.

Neither of these names were used to label the medieval Occitan language, that being said. A consistantly used name was romans, meaning roman language. Thing is, it's the same name that many other romance language used for naming themselves, such as romanz for medieval French.

Still, in southern France as in northern regions, specific names began to be used : proensals and lemosins meaning provencal and limousin.

Territorially speaking, Provence and Limousin are pretty much limited in size and location, and never were used as a broader geographical name.
But they were used for naming medieval Occitan for two main reasons.
For what matter provencal, early linguists remembered that southern France used to be a distinct set of Roman provinces and giving their population used a different language from both French and Italians, they called it "provincial". Giving it was used largely by scholars, it had a lasting usage and Provencal in an historical context is virtually synonymous with Old Occitan.
Limousin owes its use to being the main dialect of a lot of troubadours, but as well being a land from where a lot of settlers in Catalonia and Valencian Country came from.