Can not even allocate a payment!!!!

I have been trying to allocate a simple payment to my account for almost a month now with absolute no success!!! I made this payment in the beginning of April with the correct reference numbers to the correct account. After I med the payment I still received calls and sms's saying I am overdue and that I am even being handed over to the credit bereau. When I phoned the first time they could not find the payment so I sent the proof of payment to the first email address. After a week or so I still received call and sms's stating no payment has been received. I phoned again with no success to allocating the payment but promises that it will be sorted by that monday. Another week passed and still I received sms's stating I am still overdue!!! So once again, I phoned to sort the issue. Sending the proof of payment to another email address where they said it will be allocated and sorted. Now at the end of April when I paid my account thinking all was sorted I saw that the amount was still not allocated!! How is it possible to not allocate one simple small amount!!!! The service is absolutely terrible!!!