Made payment but they don't pick.it up.

I have made payment on my account via the app the money went off my bank account but somehow they never got the money .I have been on the phone with them whole week they keep saying I must send proof of payment which I did I'm highly upset because should they say they did not receive money by month end they phone me or It affects my credit rating which is so unfair.I have made payment the 10th august still waiting on feedback