TCL MT40x Not Working After Upgrade

I purchased a TCL MT40 children's watch from Hepsiburada on November 11, 2021, at 19:44. Just two days after the last updates, the watch stopped turning on and refused to charge. Previously, when calling the watch, it would ring once and then immediately switch off to busy, among a few other issues. It also displayed a self-heating warning on a few occasions, leading to shutdowns. Upon searching the internet, I discovered that many users were facing similar problems. Since the warranty has expired, we decided to retain the watch. We extended our phone line warranty for an additional year, limiting its use to this period only. However, if the SIM card is inserted into another phone, we anticipate losing access to our line shortly.