My Airtime Disappeared

I took advantage of the R10 special that MTN is running and bought it on Monday. Then I bought airtime which final amount was R67 on Monday. Yesterday I had about R63.77 and I had free minutes and free data from the special. As I was using my phone the free data depleted so I decided to restart my device. To my suprize I still had the free minutes however my airtime was gone, I was given the R55 &10mb & which expired 23:59 last nite and now my airtime is gone and I tried to call the 173 with no luck from yesterday 19:50 till now I haven't been able to get through. I did again buy the R10 special so I can log on this complaint and hopefully it will be attended to cause clearly I won't be able to log my fault through the call centre.