Company is dishonest

Today I went to the store to settle my account which was in arrears and the lady assisted me told me what I should pay and I pay it in full. when I ask the paid up letter she call their head office and they told me my account is handed over to the lawyers and when I contacted the lawyers on ********** 000 they told me they do not have my account with them and they never had. went back to sterns asking them why did they take my settlement payment and refuse to give me the paid up letter they only told me they will investigate maybe I still owe them.......WHAT A NONSENSE after I paid them what they ask for me. you cannot give a client a settlement payment and after you receive your money you come up with stories. I WANT MY PAID UP LETTER AND REMOVAL OF MY NAME FROM THE BEURO.