Premature deletion of SIM card

I have two prepaid SIM cards that I use infrequently.In order to keep them active, I use them at least once every six months, as previously instructed by Vodacom.I last used them on 10 May, and I used them again last night, 11 November.The one SIM card worked fine, the other failed to register.<br> <br> I queried this with the call centre, and was told that it had been deleted off the system.This raises three problems: <br> 1. The card was deleted prematurely - if I miscalculated the 6 months by a day or two, it should still be within the one-week grace period to restore the card