Airtime disappeared from the phone.

On the 17th September 2015 I bought airtime and sent an sms which should cost around 80c peak times. Did not make any phone calls that can deplete the balance, however on the 19th September 2015 I was checking my balance only to realize it's 2 cents left. Then I called customer care then I was told my phone received calls and it diverted them to my other phone which resulted in my airtime being used up. All these do not make sense since 1stly I've never heard of diverts costing money, 2ndly my phone did not divert calls since it was not off, thirdly if my second phone received calls why is it billing my first phone because the caller is already being billed to call me and I didn't hear any warning that I'll incur charges for the call I didn't initiate. I am disappointed in vodacom and the way they just tell you their system shows that it's a divert that caused this debacle and hinting that they will not assist me get my airtime back.