Hi
First of all, as it's indicates in the forum rules, please post your question in English to allow each user to understant your problem and potentially help you.
In Matisse there is no automatic solution to cancel double points. If the points are duplicated that means your input file has got duplicate points or the precision is not sufficient and the problem comes from a truncature error.
Matisse shouldn't generate flat elements but sometimes the trinagles are very thin. But there is no solution to solve this problem except to modify the data.
You should know that matisse is not longer maintained or developped. Try to use Blue Kenue instead.
Hope this helps