Overcharged and ****med

On the 29th December 2016 I went to a cell c store at Jubilee mall for an upgrade on my dad's contract. Took the Huawei P9 lite that was advertised for R189 on the booklet, my dad who is a pensioner asked the consultant not to add anything extra because he doesn't understand them and he's not interested, at that point we just needed to get me a phone as my phone was ****** the previous week, He promised that there won't be anything added on the mobile contract. February 2017 when the first debit order went off it was R387.99 and not the R189.99 that I saw on the booklet. I checked the papers and the invoice papers said R189.99 and the other paper said R329. I went to the store and they told me the matter would be fixed and it wasn't, they kept on deducting R387.99 then in June 2017 my father became ill and I was give power of attorney over his finances. Went back to the cell c store with all documents including those stating that I have power of attorney but the consultants refused to assist me and said that he had to come to the store and tell them that he wants to transfer the contract to me. Ooh by the way this is someone who is bed ridden and can't even talk. They still continue deducting the same R387.99 despite numerous attempts to get them to sort this matter out. Tried the call centre and they also kept sending me from pillar to post. The phone according to their papers cost R5299 and cell c is supposed to deduct R328.99 for 24 months (incl. VAT) meaning that cell c is selling the phone for R7895.76 gaining and extra R2596. Then now they deducting R 387.99 for 24 months (incl. VAT) making that a total of R9311.76 meaning that they are gaining R4012.76. Due to this wrong deduction amount. All I need to know is how do I solve this matter and cancel the ****** contract because i can't work with people who ***** my father's money and see nothing wrong with that. It's been 15 months since I took this contract and have already paid R5819.85 again cell c have gained an extra R520.85 from ******** a person who is bed ridden and cannot fix this matter themselves.