Mtn poor service

I took a contract upgrade in August 2020(IPhone) 3 months down the line the phone is not charging. Took it back to MTN (Protea Glen) for them to repair or replace in December. I have been keeping to my end contract since but not receiving a service from MTN. Today i receive email to collect the phone from the store and was not fixed. The lady assisting me is Khanyisa does not have answers for me but yet can not refer me to her senior to assist me. Im so frustrated with MTN having been with them for the past 18 years.