BAD CUSTOMER SERVICES

I had 2 cellphone contracts with Cell C and paid them in full on the 31 May 2017 now I am applying for Home loans only to find out that it still appears on credit bureaus that I owe Cell C, now I am calling Cell C to send me paid up letters for both contracts, the person I was talking to was rude saying I must ask the bank which account is that, where as I gave him my ID number he should have all the information there, I am disgusted the way they treat their customers. Your help will be much appreciated