Closed account still being looking for a debit order for 2 years

I have had a contract with vodacom for about 15 years... I never had problems with them... The last 4 years was the worst experience I have ever had with a cell phone provider... I paid up en and closed my account with them... 2 years down the line they want to send n bill saying that I have to pay.this is now after the account has been closed for 2 years... With a email from vodacom stating that everything is paid up and the account is closed... Now thay want to send my a bill for the last 2 years that I did not pay..so a must pay for a account that I don't even have anymore... Useless I tell you...