Bad Service No Regard for Customer!!!

I wish someone at MTN can just help me cancel my Home of Internet service. I returned the device to the store 3 months ago, it is now end of July and I am still getting billed. Please can someone just help me please, I beg!!! The call centre refer me to the store, the store refer me to the call centre. I am just tired from all this up and down MTN!!! Please cancel the contract!!!