Mtn
Data dissapears

I use my data only to download emails, 90% only data, no pictures, so small emails. the last 4 recharges of 300MB just disappeared. sometimes even when locked off or even while computer is off. previously 300MB lasted me 6-8 weeks, now not even two weeks. I phoned mtn and they promised to investigate but I did not hear anything back in the promised time. phoned again, been cut off twice. I recharged again today