********** my airtime

3 months ago my mom recharged with a 100 then received a message that she has free minutes from mtn which is not true because you use the stupid airtime they put then when it expires it took her whole R90 which she was left with then when you call the call centre there is no answer for hours of holding. The other day she got some message about some free 500mb if she joins music plus something which I joined for her and got the free 500mb which is unusable on internet or on whatsapp which was not even mentioned when I joined that the data is just for listening to music. Today on the 16th I buy R10 airtime n convert to data when I check her balance it says 550mb but she still can't use any of it. Can someone explain what is happening with mtn cos this is frustrating. I'm even convincing her to change to another service provider.