Lack of in store knowledge and procedure

I requested a settlement balance from Tenacity after much confusion from the call center or customer service or customer care whatever the hell it's call because they are neither, helpful, caring nor worth being called a service. None the less I received a letter from Tenacity stating the balance. I attended the Ackermans Westgate mall (Mitchell's Plain) with the intention of settling this balance. On the same day, but before settling the account, I returned two pairs of very sad, unwearable tights I had purchased. Giving the tights to the cashier, she credited the account. She, however, still deducted the full settlement balance (which was now supposed to be less now because of the tights), which was not her fault, I don't think. I checked the till slip which now displayed a credit balance due to me. The cashier then call Wendy, the store manager, who said that the error cannot be fixed in store and that I should just take something to that value and it would be cleared up. After I declined that, because how did she know that I did not need that money, she then put me on the phone with Tenacity and I spoke to Mihle who explained that I would need to send a bank statement in order for them to refund my money and this could take 3 - 5 days. Stupid system though. My problem is with the in store service I received. My question is: was it not possible for this problem to fixed in store? Was there not a generic SKU which could have been used to ring up a "sale" and then credit that same SKU for that exact same amount and me getting my money back immediately? And Wendy cashing up the cashier in the evening having balanced? I am now out of pocket a certain amount because of Wendy's "simple solution". After all of this drama I eventually ended up taking unnecessary items as I wanted nothing further to do with Ackermans and closed this account. Today I was presented with a statement of account. Noted that invoices have been generated already, I request that you check you records and update this whilst investigating my complaint. This is not the first time I encountered Wendy's lack of professionalism. I previously had to hear of a party she attended and then called it "work related" but telling the cashiers to keep their conversations for the taxi. The reason any store loses business is due to "customer care" call centers.