Unresolved Warranty Hassle with Gulf Insurance

I bought a tablet from Teknosa and got the TechnoGaranti insurance. The screen is cracked. After I sent it to the service center at Teknosa, they told me that I could get the screen replaced for a certain amount of money. I asked for it back and sent it to Gulf Insurance with TechnoGaranti coverage. Gulf Insurance said they couldn't fix it, so they gave me an 1199 TL gift voucher from Teknosa instead. Also, they took the tablet. It's so silly; screens can be replaced anywhere, so how is it not possible? I want to complain about Gulf Insurance and Teknosa because of how they have been behaving.