quick question on top up?

I am on a 99topup and haven't used the sim for 8 months.
Every now and then i just check the balance.
Sometime December VC forfeited R200 from my account.
Seems now the R99 is only valid for 6 months.
I thought you can only forfeit Free minutes not airtime.

Did VC suddenly changed its TOS for topup or has this always been the case?