MTN vanishing airtime

Recently I have found that my prepaid MTN airtime and data is getting exhausted more quickly, sometimes even without making any calls or using data. I bought R60 airtime and 100 MB data from FNB online services on 19 May. I made only 2 calls that week and on Sunday 24 May I find that I am left without any airtime and data. I recharged with R60 airtime Monday, 25 May. I made sure that I made no calls from my phone and when I checked my balance on Tuesday, it shows that I do not have any airtime. I use Wifi at home and work and hence I switched off the data on my phone to be sure that the airtime was not consumed due to enabling 3g data. I recharged again with R60 today, Wednesday, 27 May at 9am. I made 2 calls, which lasted a total of 7 minutes. The data was already turned off. When I checked my balance at 11am, I am left with R0.01. I checked online and found that WASPs can explain this, but using *141*5# I have checked that this is not true in my case. MTN Musgrave Centre were unable to help me as currently MTN is on strike indefinitely. Is this some kind of ***** which is prevalent with MTN? And what happens to the my R180? (it could be more as I didn't check before this week)