Impossible to cancel

It seems it's impossible to cancel an account with telkom. I emailed a cancellation form through as per the instructions on their website on the 19th of February. So according to a standard 30 day notice period my account should have been cancelled 19th March. I also went into the telkom shop, phoned the call centre twice and used their online chat in order to cancel again when I received an invoice in march, April and now again in June. I paid up to march but now I refuse to pay as I cancelled in Feb and signed up with a new service provider in April. Telkom how do I get rid of you??!