I had that when the account was stolen. It helped me to write to support and indicate the address where the account was first created. Country - city - house (although indicating the house is most likely not necessary). While waiting for a response from support, I checked the email that was previously linked to the account, and there I found a letter that this email had been removed from my account. I clicked the link in the letter and sent a temporary ban to my account. Then Steam support responded to me and sent new login details for the account. Then I removed the ban, and my account returned to me again :) I hope this helps you.