Rip-off by ONEPLAN

I had a policy with ONEPLAN no. ********** 05 which was cancelled on the 28 Feb 2018 with the last deduction on the 15 Feb 2018. I received an email to this effect. The email correspondence also included the cancellation fee of R100. The basic logic is that all that would have been taken off my account with the last deduction. There was no mention of an outstanding amount which my simplest understanding suggest that they should have noted and taken it off before a cancellation be effected. Today 14 Nov 2018 I received an sms from a debt collecting company that OPNEPLAN want me to pay the outstanding amount of R259.50. They have not furnished me with such correspondence that I owe such an amount but decided to use a third party without contacting me first. The fact of the matter I feel that my rights have been violated as the consumer and that legally I do not own them.