[Q] Unofficial ROM, CUSTOM ROM - Service said it cant be repaired topic

Hi!
I bought this phone on the internet and it was rooted, had no google play on it. I unlocked it via a website, then tried to install a custom ROM from here. Since, it cant be turned on, took it to the service, they said its cant be repaired. The seller wont pay me back my money, because they said i made it wrong.
Do you have any idea what to do now? I have no phone and paid much for it :(