Contract cancelled(Paid-up) still receiving invoices- legal notices

I was told my contract could be cancelled at the end of February 2018, i provided them with notice and i still received a statement. I was then told my account was in arrears, i provided them with proof of payment as i have never missed a payment. I am now receiving final notices to pay. I have been in contact with vodacom every single month. i was told the issue was escalated two weeks ago and i have still not received any feedback. We as consumers have to take time out of our busy schedules to deal with incompetence in certain departments. i have been sent from pillar to post and nobody can give me a straight answer, and now they are threatening to hand me over as my account is already in pre-legal status. I as a consumer have kept my end of the contract by religiously making my monthly subscription payments, gave sufficient notice to cancel and now have to deal with *******.