Xiaomi Smart Phone Doesn't Show the IMEI After Only Five Months of Use

I bought a phone from Vatan online, and they sent it to me from their branch in Konya. The device not only doesn't show the IMEI after only five months of use, but it also has a lot of software problems. I took it to Vatan's warranty service because I was angry, and the process seemed to be moving forward. After some time, I got a call from the warranty service. They said they found unauthorized software on the device and needed ₺5400 to fix it. I was so upset about this; my money was wasted, and the phone can't be used anymore. Vatan Computer has been terrible at handling this situation, and their ridiculously high repair costs for a problem with the way they made the computer are not acceptable. I feel ripped off and cheated by the quality of their service and product.