Unjust Account Ban by GamerMarkt

Months after selling my account on GamerMarkt, I was banned from using third-party software. I had to go through authorized channels to have it reinstated, reclaiming the account I invested three to four years of my gaming career. There's no one at fault here, yet GamerMarkt insists I return the account for no reason, threatening legal action. A wealthy individual gets my hard-earned account banned through cheating, and I'm the one deemed guilty when I reclaim it. The price they're asking to return it is nearly double what I sold it for. GamerMarkt has caused me a lot of distress. When I had the account, I purchased around ₺1000 worth of costumes. I demand their return and the reinstatement of my account.