Out of the blue arrears

I had an account with vodacom and I settled the amount for my phone they sent me a letter with the settlement amount and i have not even been using their simcard. They removed everything on the bureau now all of a sudden i get an email that I have arrears of 360 something on the account that i settled i sent them an email and no one is communicating back and these arrears are messing with my bureau score that i suddenly have arrears on an account i am not using this is absurd and if vodacom is like this i would never recommend anyone to take out an account by them