They are useless

I have been getting calls/sms's everyday asking me to pay my account. I have sent emails with proof of payment and have spoken to numerous people regarding the matter but the one is just as useless as the next and when I ask to speak to management I get told no I can't as they are going to tell me the same thing.The attitude i get from the staff is also something that needs to be addressed if you want to grow your business further. I got a reply on one of the emails saying they found the payment and are allocating it but haven't received any feedback which I have asked for on all the emails sent to them. Just my luck I woke up today with another sms regarding this matter. Who do I speak to to sort this out as the call center/ customer service is useless as I have previously mentioned.