Vodacom ignorence and incompetence

I upgraded my contract with Vodacom in November 2020 and received one handset, althought Vodacom charged me for two handsets. After a long struggle, the devices on my account was changed from two to one, but the payments I made for two handsets was never credited to rectify the account. After numerous e-mails and calls to Vodacom, the account is STILL not corrected. Instead of Vodacom correcting the account and giving me the credit that I paid for after being incorrectly charged, I am no getting threatening letters regarding the account. Vodacom **********ly charge me for a handset I DID NOT RECEIVE and is maybe to *********** to fix THEIR mistake. I feel this is extremely poor service delivery and will not pay for Vodacom's negligence!!!!!