What to do when some students pay someone to solve their exams projects and thesis?
I will take a wild guess and speculate that the university referred to in the question is in a country that has high levels of systemic corruption, as measured for example by Transparency International's Corruption Perceptions Index. Countries near the bottom of this ranking have the feature that most if not all of their main institutions experience high levels of dishonesty and unethical behavior. That sounds consistent with the OP's description, and conversely, in countries that rank low for corruption it is hard for me to imagine an academic environment where such rampant large-scale dishonesty could be practiced with impunity by so many people and tolerated and ignored by so many others.

Assuming this premise, I find it helpful to reframe the question as a broader and more general one, that would contain the OP's question as a special case:


  What should I do if I am an honest, hardworking person who wants to learn a trade, get an honest job, be judged for my abilities and become successful thorugh talent and hard work; but I live in a country with such high levels of corruption and dishonesty, and such dysfunctional institutions, that I see people all around me getting ahead through cheating and other dishonest means, leaving me no practical way to realize my dreams in the honest way I wish to?
  
  Should I try to fight this behavior? Should I try to find a rare honest person around me in a position of power to complain to about the dishonesty I observe? Will this change anything?


My answer is probably not a very helpful one, but I think it is the only realistic one: leave. The forces you are trying to fight are so much bigger and more powerful than you, that unless you are willing to dedicate your entire life to fighting them, knowing that you will achieve either nothing or very little, your only other choice would be to keep your head down, either ignore or join in the cheating, and resign yourself to a life of dissatisfaction and unfulfilled dreams.

Sorry it's pessimistic and depressing, but there it is. I would probably vote this answer down myself if I could. :-(