Being harassed for money already paid

My husband made a payment via EFT well in advance but used an incorrect ref no so payment wasn't allocated to my account. RCS asked for proof of payment and said they would allocate the money to my account. I tried emailing it through from different e-mail adresses literally about 10 times but they kept saying they aren't getting it. I eventually had to go into a Coricraft store to ask someone there to fax it for me. <br> RCS confirmed they received it, this was a week ago. However it STILL hasn't been allocated to my account and yesterday I received calls from the collections department harassing me to pay - not just the last instalment, but also the one only due by 1 Oct. I told them I already paid but was still being asked to set up a debit order and being asked when my salary gets paid and when I'm going to pay the one due on 1 Oct. I even got an SMS at flippin 2am asking forthe money. I don't appreciate being harassed and treated like a ******** when the payment was made but due to the incompetence on your side, the payment hasn't been allocated yet. I also CANNOT be charged extra, like interest. Please rectify this IMMEDIATELY and stop contacting me!