airtime,data issues

I am so sick and tired of mtn using up my airtime and data. Like today I topped up with R5 then bought data just seconds after buying data I get an sms saying my data has been depleted and they try cover it with this R15 free airtime and data and 15 MB so I won't see it. This is not the first time my airtime disappeared in seconds I am tired of this. I thought I would be happy with mtn but I get problem after problem...goodbye mtn I am exporting my number to cell c because of your bad service will tell my mom to stay away too because you rob your customers