The overwhelming evidence supports that Genghis Khan existed, but there are several inaccuracies that I would like to address.

the fact the only people who talk about him were the Mongols

This is absolutely wrong. One of most notable aspects of Mongol historiography is that the Mongols, similar to most tribes from the steppes, wrote very little about themselves. A written script for the Mongolian language didn't even exist (if we exclude the Khitan adoption of Chinese characters, but the relationship between Khitan and Mongolic is controversial) until the Mongols adopted the Uyghur alphabet under Genghis. This is why most of what is known about the early Mongols, the Xiongnu, and other steppe empires comes from accounts written by scholars in agrarian societies like China. In fact, The Secret History of the Mongols, the most significant contemporaneous source about the Mongol Empire written by the Mongols, actually only survives as part of a Chinese compilation dating back to the Ming dynasty. The original Mongolian version is lost.

now the Chinese didn't have much written about him

This is also erroneous. The opposite is true. Much of what we know about the early history of the Mongol Empire comes from Chinese sources. The Jin dynasty interacted with the Mongol tribes prior to Genghis, and the Jin bore the brunt of the early Mongol invasions. The Chinese were very detailed at keeping records and the literary elite within Chinese society produced thousands of texts. Several battles with the Mongols and diplomatic records were documented by the Jin and Song dynasties. Few of these sources have been translated into English, but they are accessible to researchers.

The Chinese records can be very revealing. The Yuwen Maozhao's Da Jin Guozhi, written circa 1160, states the Mongols were originally a vassal of the Jin dynasty. This was no longer mentioned once the Mongols took over, so some historians have speculated that it was removed by the new Mongol rulers. Either way, it shows that there are extensive records from the Jin and Song dynasties that describe the history of the early Mongols, even prior to Genghis. It's completely absurd to think that the Chinese could have concocted Genghis Khan, and no reputable historian has ever suggested that he didn't exist.

Yes , Persian Muslims wrote lots of accounts about the Mongols like the account of Tarikh-i Jahangushay Juvaini http://en.wikipedia.org/wiki/Tarikh-i_Jahangushay-i_Juvaini and many more from Khwarizim writers and many many more also he can't simply be a "myth" but it rised a doubt because of the "Secret History" of Genghis Khan and where is he burried etc..

In short, the records you may desire to exist simply don't exist, and there's no reason for them to. There's ample evidence of the invasion itself, and that's about all there is to know. The Tarikh-i history mega-t mentions is a Middle Eastern source, but a generation removed (relatively close to events, all told) and exceptionally friendly to the Mongols.

What you're looking for is, are there records, concurrent with Chingis' reign, in which reliable people who are not necessarily directly sympathetic to the Mongols say they met Chingis Khan, face to face. To my knowledge, no. If such a source exists, it's from the Xia or the Jin, and my knowledge of Chinese primary sources is, well, nonexistent.

This really shouldn't surprise you. Mongol conquests were often accompanied by the abject destruction of existing power structures and Mongol rule is characteristically hands-off. Surrender to the Mongols meant basically no Mongol presence at all. Chingis was not parading around like a cartoon villain, monologuing to Chinese officials. Nor was he a European folk king, leading cavalry charges and breaking sieges. He gave orders, won battles, planned yet more battles. The Mongol Empire had nothing approaching diplomacy.

You could make the same argument, but more convincingly, about virtually every Chinese emperor, since they were members of an organization that, in size, scope, and age, dwarfed them absolutely. The utterly disorganized Mongolian steppe, over the course of a generation, became the nerve center of an empire that taught the Chinese a thing or two about being officious and assiduous. The locus of this centralization was the father of several powerful world leaders, of whom very much is written, and long descents of world leaders on two continents.