calling the call centre for answers but no answer

i have loaded air time on Monday for 60rand on top of the money i had in my account but all that airtime was gone on Tuesday and loaded again airtime on Wednesday and are few minutes later i bought 10rand worth of sms bundle and the rest of my 30rands airtime was gone, when i called the call Centre the 1st person saw my airtime on the system but could not tell me what happened to it but now they tell me i did not load airtime for 30 rands because the cannot see it and still cannot get answers of what happened to my airtime, because they transfer me but the number does not go through, still waiting for the manager to call me because that is what i was promised but still nothing. scared to load airtime now because it just disappears with no answers from mnt and on the other hand i cannot stay with out airtime on my phone in case of emergency.