Problematic phone

My mom purchased a Huawei phone and has been having endless issues as it keeps switching off by itself and when you switch it on a foreign screen appears. This has been going on for the past 7 months and she took it to Huawei Melrose arch a month ago who kept the phone for the week and had to resest the entire phone. Again same problem, can someone pls help as she needs her phone for business???