Unallocated EFT payment into

I have made an EFT payment of R2500 at American Swiss at Fourways in favour of my RCS account to bring my account up to date on the 20 February 2018. To date my payment is yet to be allocated to my account for reasons which are yet to be fully explained to me. I have been calling RCS since then asking them whether my payment has been allocated but I was told that the merchant department is yet to allocate the funds. I have been receiving calls from Brendon and Ashraf from collection requesting me to make a payment when I have made a payment which they are yet to allocate to my account. Later my account was handed to debt collectors and I have been receiving emails and calls from debt collectors harassing me to make payment or else face the consequences of the law. I have not made any payment since then since they are yet to allocate the payment I have made, they continued to charge me interest on the money I owe to them ignoring the payment I have made. This has affected financially as I had to call them almost everyday to find out if the funds have been allocated to my account and also affected my credit score..