no information/on costs involving changing contrac

we went to mtn in November 2014 for an upgrade on my husbands phone,we decided that we want a laptop instead of a phone on the upgrade,the supervisor was very anxious to help us with this upgrade ,we did inform him that this laptop Will be used in Tanzania ,they gave us a dual Sim with the same number one for the laptop and the other 1 for the phone,and he said no problem everything will work ,it is know February and the Sim for the laptop has never worked and all they say is sorry and at the end of January we received a bill for over R10 000 and we have hardly used the phone ,my husband uses it to contact me but I came to visit him for 2 months so the phone was hardly used the miniman calls were made.They charged us between R23 and R55 A MINUTE WE have sent in a Query several times and the only reply we have received is .Dear customer we have received your complaint and will contact you as soon as possible,it is up to date 5 weeks since we have lodged this complaint and no reply,we searched on the Internet on mtn for roaming billing and nowhere in any price range was there an amount that they have charged us .No response from mtn please help.