service cut short

I've app**** to get my SIM canceled and was told that I needed to give a 30 day notice. This was a few weeks ago so I accepted that the SIM will be canceled the end of September.<br> <br> I've received a phone call today on @ 10h32 the 28th August for 8m10s. He said that the SIM will be cancelled but did not say when. After the call my SIM stopped working. This was a surprise as there are still 3 days left for the month. I've payed for a months service. Will I be billed pro-rata for the month and DATA used as I still had more that 3 Gb left on the SIM?<br> <br> I've signed the paperwork on the 31st of March 2015.<br> <br> This really make is look like the service providers try to ***** us here they can.