Bad taste in my mouth

Rcs PNP,you guys has the worst customers service! I ask for a settlement letter on the 5th letter is valid for 5 days.Paid in full the next day.On the 1Oth I ask to close my account ,couldn't first reason was it was arrears since October then the back and forth began.The next day I phoned again then the lady said I skipped a payment in January and it was given over to a firm,coz payment doesn't reflect.i called again the next day no one can give me answers where my payment went.i emailed proof of payment no one is emailing me back!in the meantime threatening emails and SMS keeps coming through,and the balance keeps growing!!why the settlement letter then?