Double Debit on a new line

I have an existing contract with Cell C for the past 5 years, so last month (2weeks ago) I saw that the Blackberry Z3 was at a decent price with a good package and decided to go for it. Yesterday when i logged into my bank account I was surprised to see that they had debited me twice for the new line. I queried with the branch manager who said that it was a store fault, they has \mistakenly"activate 2 lines for me when they processed my new contract. anyways later that evening I was told by the manager to contact the call centre if I wanted a refund as my account is now sitting on credit for the duplicate amount debited. Call centre logged everything and advised me that this will take 21 days to resolve. Really!! this will be in time for my next debit! as if that is not enough"