Being forced to pay the account that was closed

I had an account with MTN for over 10 years, on the last upgrade I had a financial problem towards the end. Eventually I paid and closed the account in 2009. In 2010 I got a call from MBD that I owe MTN the money the has not been paid. I went to Soweto MTN branch and they checked and Identified as the payment required from new onwer of the number. I was cleared and I stopped getting calls from MBD. This kept going over again at the rate of 10 months intervals. This has started again and MBD are forcing me to pay they tell I owe MTN and I must pay. <br> MTN can not tell what do I owe them. the cancellation happened in 2009/2010. All the term of the contracts were honoured.<br> So what do I do to come out of this.<br> <br> MTN and MBD know how harass people.