*****ing (paid for) airtime from customers

I just checked my balance seeing that it is the 1st of the month...***? Yesterday i had over R1000 and today I should have had R1200...now I only have R600...phoned and they say some forfeits after 6mnths? I paid for that airtime who gives them the right to take it? We have an account for R2870 a month...from now on every single contract that needs upgrading we will cancel...this would be the last time vodacom *****s from us ?? if there was an option they would get zero stars