Angry MTN customer

I want to hereby express my absolute dissatisfaction (to put it mildly) with the service I have received from MTN. Bought a Samsumg s21 via online which gets hot while I use it and I have hardly had it for two weeks. Phone calls, video calls, taking pictures or videos cause the phone to heat up. Been trying to contact the online service ever since to no avail. Finally decided to visit the Baywest branch in Port Elizabeth where I was referred to the main branch in Cape Road. Upon my first visit I did not have the box and delivery note which is my fault of course. The gentleman assisting me advised that box was needed but the note was not integral and had I had the box he could have assisted me with a warranty assessment. Alas I had to return the next day with box unfortunately same gentleman was not there and the women who assisted told me that she could not help me without the delivery note/invoice. I then proceeded to ask what would happen if I could not find it to which she rep**** then MTN could not help meaning I would be stuck with a brand new 'top of the range' cellphone purchased from MTN not even two weeks old which is faulty. Suffice it to say that I am not happy as I have it on good authority from the Baywest store that the lady who assisted me could have just printed the invoice from system. Also awaiting assistance with query ***. I try wish that someone at MTN would please do the right thing and assist me this problem?