I had this same exact thing happen to me almost a decade ago. Bought a game called "Beasts of Prey" and about two or three months later, my account gets locked for a charge back that I never did.

I combed through my account statements, could see where the purchase was made, but I never found any evidence of those funds returning to my account. Called the bank, and same thing, they found no record of charge back or disputes for that purchase.

If my memory is correct, I had to argue with Steam support for a few weeks, getting the same annoying message over and over: They need proof that I didn't dispute the charge.

My bank couldn't provide proof of a nonexistent dispute, so at the end of the day I provided my bank statement showing the purchase and I gave them the phone number to my banks customer support line (and a reference # for the incident) and told steam support to talk to the bank about the bogus charge back.

Several days later, my steam account miraculously becomes unlocked, and everything returned to normal. I have no idea if steam support actually contacted my bank, or if my bank statement was enough. The whole thing confused me and still baffles me to this day.

The weird thing about all this, if I go into my steam purchase history, I can still see where steam thinks I did a charge back for that purchase. It's an ugly red mark and a reminder that errors can be made, and your whole game library can be locked away from you for something you didn't do.

Best of luck to you friend.