Extremely dissatisfied client

Very unhappy with the service im currently receiving from them. Its been a month now constantly trying to resolve my inquiry and none of them is helpful. Got an additional contract for a samsung tab 10inch in September 2020 which in January did not want to charge at all. With a lot of hassles i eventually send it to an mtn store as it is still u der guarantee which i did not do anything for the tablet not to charge. After 2 weeks they said that they will give me a replacement tablet with no additional charge which they will on there side just do an early upgrade as that is the only way they can replace the tablet. On 5th of April there was an additional amount of R4500 plus vat added to my bill which im just not successfull to sort this out. Trying to phone them which the one consultant transfer you to the other one from retentions and then the billing department that takes about an hour on the phone with no one answering. They blocked all my phones because i did not pay that amount and it was not agreed on and with the constant struggle after a month now no success