Paid yet Keep getting threatened!

<p>So first I get an invoice with no reference number to pay it. Then I finally get an sms demanding I settle my account together with a reference number. Now three months later nearly I keep getting invoices and threatening sms' that I have not settled my account. I even phoned yet the issue is still not resolved! </p> <p> </p> <p>I paid you! Stop bothering me and do your admin!</p>