Poor service received

Last year I opened a new contract at Vodacom Westgate. Vodacom made an error and debited my account with the full contract amount as a single payment. I reversed the debit and it took me three months to sort out this mistake of Vodacom. On 27/11/2018 I tried to open an additional contract. My application was declined due to the returned debit order, although it was not my fault. All my accounts are up to date. I phoned Vodacom numerous times to clear this block from my name so that I can apply for a new contract. They send me from pillar to post. I logged a query in December and till now I have not received any feedback. Today I tried to open a new contract, but I am still blocked. The sales person did not know what to tell me. This is very unprofessional as it was Vodacom's error in the first place.