Insurance was not cancelled

I didn't renew my cellphone phone contract years ago when they called me for an upgrade and now I receive statements that I'm behind on insurance on the handset.

I remember they were owing me but they did pay as I never changed my stop order when I took a phone Which instalment was lesser than the first one.Then when I had to upgrade again I didn't but requested termination.

I even lost that phone years ago,why didn't MTN cancel the insurance as I have asked when I terminated the contract?Such a big company and they are