MTN *****ing from it's customers!!

I went to MTN in N1 City Mall to get my upgrade. When I walked in there, I knew which phone I wanted, which was the Huawei P20 Lite. The consultant who assisted me from MTN along with a consultant from Huawei then tried selling me a different phone, which was the Huawei P Smart 2019. As a customer I listened to their opinions, but the decision was still mine at the end. But due to the fact that they "sold" the P Smart so well, I decided to go with the P Smart rather. According to them the P Smart was/is way better than the P20 Lite and I wouldn't make a mistake by taking the P Smart. About 2 days later of having the phone, I realized this phone is nothing like how they "sold" or described it to me. The phone was slow, freezes up, settings changes back automatically to its default settings, etc. Unfortunately I couldn't go back within the 7 day period so they had to send the phone in for warranty repairs. The warranty repair was approved and they told me I can come fetch a new phone. They first didnt want to exhange it for a different phone but then eventually when they decided I can get a different phone, they told me that doesn't matter what phone I take, my contract will stay the same. Which means in my case I eventually took the P20 Lite, but my contract never changed, so now every month I am paying more for the phone then what I am supposed to. How is it possible that they couldnt change my contract and now I have to suffer and pay MTN more than what I'm supposed to for that phone. As a loyal MTN customer I am very disappointed and disgusted in this kind of service and as for that I will be thinking twice of upgrading again with MTN. Not only is it bad customer service, but MTN is literally *****ing from it's customers!!