Why was I denied service?

Can anyone explain this.

I received a notice telling me that o/g service would be disabled as payment could not be collected, despite auto-renew being active. Logging into my account, I noticed that my data allowance was 0Gb, yet my next month's bill showed a reduction because I had not used up my data for this month.

Also, is there ANY WAY you can get to speak to someone by phone?