Higher Pricelock rate charged, despite the contract coming to an end

My Pricelock contract with DSTV came to an end on the 30th December 2017, however DSTV is still charging me the increased rate for the pricelock contract. I have e-mailed and phoned DSTV on 3 occasions and am still getting no response from them as to correcting the mistake on their side, instead I get a call from them on a Sunday trying to sell me a new Pricelock contract. Be very careful when taking out a Pricelock contract as they seem to not want to end the contract and reduce your billing back to the reduced rate after the contract ends.