Gabelein Bros Septic Plumbing

I contacted Gabelein Brothers Septic to pump my septic system and the company responded promptly. I arranged to have the service done and when a crew came and pumped my tank - I paid them for the full amount with a check upon completion. Approximately 30 days later a bill arrived in the mail for the pumping service. I called the company and said I had already paid them for the full amount and explained the check had cleared my bank. They had received full payment. The person I spoke with said please text him the check number and this would be taken care of "no problem". One month later I received another bill in the mail. I called the company again. The same person said send him a phone text of the check number and the matter would be taken care of. Yesterday I received another bill in the mail with a notice that if I failed to remit payment - the bill would be forwarded to collections.
I have made repeated attempts to resolve this issue with this company. I have documentation of my payment and efforts to supply information they requested. Their failure to reasonably take care of this matter is why I am filing this complaint. Any assistance from your organization would be greatly appreciated.