DATA sim app**** for but up to date has never been received but i have been paying for it since march 2017

My husband who is the main account holder of our cellphone contract was offered what seemed to be a good deal earlier this year. they offered a data sim which was to be delivered to us but it never arrived. we are unfortunately being billed monthly for this mysterious sim but we have never used it. we have been to the MTN at pavilion, kwa Mnyadu mall called endless times to get this issue rectified but up to date this has never been rectified. they had promised to rectify the mistake and credit us all the money we have pay them but still nothing. It's almost going into 10 months but this hasn't been fixed and it's frustrating. we have kept record of various reference numbers hoping that this will be sorted but every-time we call their customer care its just another stumbling block.