Steam Account Compromised,  Documenting Ownership Won't Work

Someone hacked into my Steam account, I've lost control of it, and trying hard to take it back...I've got all the documents to show that the account is totally mine. On the flip side, I can't seem to get into my account or ask for help using the usual ways. So, basically, once the new owner took over my account, they updated my email address and phone number which kind of cut my connection with the account. Is anyone here with an idea? can you tell me where to go and how to send the info I need to get my account back? Thanks! I would really appreciate it if you could help me out with finding a solution to this problem.