Paid in advance but payment not allocated

Good day. I need to know what is going on with my billing. I made payment on the 17 April for May as I normally do but my account says I am in arrears. I contacted support and asked them to send proof of payment which I sent, to billing so my payment can be allocated. This clearly was not done. Please explain what is going on here as it says I must make payment to avoid suspension. If you require POP again, please supply email address to where it must be sent. Other than that service is very good. Thank You.