Unhappy customer

I took a contract with MTN ,it was a deal for 2 Samsungs.The other Sim is for data and the other for airtime.I was never explained how the simcards should be capped to 0 so that when the airtime or data finish and I continue using the simcard they gonna charge more.I thought if the simcard allows me to make calls or to access internet it means there's still sufficient data or airtime. I called and asked why my bill is always more and not constant and they only explained then that I was suppoed to capp to zero.I then went to the store December last year to capp the simcards,they only capped the airtime Sim and not the data Sim.Sinc3 December I have been siting with the same issue when I call or go to the store to try capp the data sim one they always tell me different stories.I honestly feel like I am being ****med at this point .I wouldn't recommend MTN contract to anyone because why do you make extra money in such a dishonest way.