Still paying for a cancelled landline

Once again I find myself having to phone Telkom or go into the store because the call centre can not assist me. I have cancelled my service at the end of August and am still being charged. I was told by the call centre that I would pay at the end of September for August? How does that work exactly? now I've been sent a bill for October? sort this out Telkom, as this happened with my contract phones as well!