Very poor service

I have a contract with intellicell and around mid March I received a call from one of their sales person offering me an upgrade I declined since I'm not working, I was advised to call or whattapp to cancel contact since month end will be the last deduction, I did so and I was told via whattapp I will receive a message once all is done, on the 20th of March debit order did not go through due to insufficient funds and then my phone and sim where blocked, two days later I received a call from one of their employees since I requested them to call me, he informs me to pay r339 and r150 for the once off fee that was reversed at the beginning of the contract, I agreed to pay r339 and will pay r150 end of April and he also confirmed it will be the last payment. On the 20 April I saw the was an attempt debit of r339 on my acc, only to find insufficient fund, when I addressed the matter with them via whattapp they denied, on Friday my phone and sim where blocked due to non payment, I thought it was for the r150 I promised to pay end of April, I called them they say I must pay r339 since my contract ended mid April, I refuse to since I confirm with two of their employees and they agreed that the March payment was the last and contract will be canceled. I have payed the r150 for once of fee but to date my phone and sim I still blocked... This is daylight *******