Accouny PAID but continue to receive letters that I have not paid it

<p>Hi</p> <p> </p> <p>I have paid my October installment of my Woolworths personal loan and have sent the proof of payment. I have been handed over to Nationwide credit for NON PAYMENT to recover the funds even after sending the POP TWICE. I have now sent it for a 3rd time! I now have a bad credit score for failure to pay. This is unacceptable!</p>