The answer to this question depends largely on which definition of matriarchy is used. But the consensus today is that we do not know of any society in history that was matriarchical in the strictest sense of the term, i.e. women holding all the positions of power and influence in a society and being placed above men.

Depending on the area of study, there are different definitions however, but more importantly the term matriarchy is often mixed-up and/or conflated with related concepts such as matrilinearity or matrifocality, i.e.social structures wherein inheritance and kinship revolve around women.

Of these we have both historical and contemporary examples, such as the Iroquois and Hopi of North America, the Akan in Ghana and some ethnic minorities in China, just to name a few.

The oldest such society that we know of in Europe, which might be considered matriarchical (again, depending on how you define that term), that we have written records of, is the Minoan culture that existed on the Greek island of Crete from 2600 B.C until 1450 B.C. It's considered the earliest "advanced" culture in Europe and placed women in relative positions of power, especially in comparison to Mycene culture of Greece at the time.

In some matrilineal societies we know of, the concept of fatherhood as such does or did not exist. Children belong to their mother's family and men (even if they have a partner and biological children) are considered part oftheir mother's - and after her death - their sister's family.

Some societies are a mix of patriarchal and matrinilineal concepts, where for example men hold all the positions of power and only men inherit, but a man’s inheritance does not go to his son, but his sister’s son. So through the female line, but with a male as recipient.

Judaism, which is a very patriarchal religion, yet practices matrilinearity in regards to religious "membership" is an interesting examples for this. Children (at least in the traditional denominations of the religion) are only accepted as Jewish, if their mother is Jewish. The father's religion does not matter, yet women cannot be rabbis etc.

During the second wave of feminism in the last century, there were multiple theories about prehistoric matriarchies put forward. Many of them revolved around the idea that matriarchies were dominant in prehistoric times, which predate written records, and then were later supplanted by patriarchial societies. These theories are based on the abovementioned concepts of matriliniearity in historical and modern societies, that we do have evidence for, as traces and leftovers of possible prehistoric matriarchies.

And there are definitely plenty of interesting and compelling glimpses of matrilinearity, that support the idea that matriarchies could have existed at some point, such as the fact that Chinese names were originally derived through the female line.

But it’s impossible to tell for sure if matriarchies ever really existed and it must all remain speculative, since we do not have any written evidence.

So as to the second part of your question. Assuming they did exist, we can only speculative on why they disappeared.

Perhaps someone else here can point you to a good beginner’s resource for this area of study. The ones I know are not in English.