Repair Centre Damaged Phone

I sent my Sony Experia in for repairs to software issues, got the phone back and lasted for about a week or two then i sent it back for the same problem. Not a week later they called and said my phone came back from repair center i can collect it in the store. when i collected it from the store i discovered that i cant enter my sim card in the slot so i sent it back for the 3rd time but this time not for software issues but for the sim card slot. Now the Repair Center in JHB phoned and told me that i must pay R2700 to repair the sim card reader which the REPAIR CENTER broke and \ I "must pay R330 to get the phone back because its physical damage even if the damage was caused by the REPAIR CENTER. It is absolutely no use having a contract with MTN if THEIR repair center caused the physical damage and i have no Phone."""