rip-off of airtime

I bought airtime R15mtn at shoprite and I loaded it into one cellphone because I have phones both using MTN. Ioaded the airtime then transferred R7of that amount into my other phone I even got an sms saying I've transferred the airtime that was after 2pm at 16:46 I called my mother also MTN and spoke for 54 seconds on the phone with R8 it cost me R0.30 when I checked my other phone the one with R7 I found that I had R0.02 left without using any airtime, yes I use the phone for surfing the Internet buy I have more than 1GB on it so I didn't understand where or what is eating my airtime??!.when I called MTN customer care the one lady I spoke to said I made a call for 3min 10s which was wrong I don't know where she dug up that nonsense,then she tells me maybe I transferred the R7 to a wrong number, yet I got a sms saying R7 has been transferred to the number,she was in a rush to get rid of me and was unhelpful! I tried to phone again this time a guy waited till I explained the whole story before telling me to use the other phone number!!! My airtime can't just disappear!!! and FYI.i am not subscribe to ANYTHING!! So basically MTN RIPPED ME OFF....dame shame