Data expiry

I would like to find out why after we pay for data does it have a expiry date and if i still have data left at 30 days does it get cancelled from my phone.

I mean after all i did pay for it so why would it get cancelled i mean when i buy something at the shop it doesn't get taken away after a certain period of time, surely vodacom should refund or extend the data that is left on your sim card if it was paid for?

To me that is tan amount to *****ing surely as i paid full price for it so surely it is my data till it is finished and cant just be taken away, i had over 1 gig of data still on my sim and today **** like magic it disappeared.

Sorry to say but this is absolute madness that we must pay actually over pay compared to the rest of the world for data and then it still gets taken away, surely something should be given back to the consumer and we dont just have our money ******, hell i would even be happy with a digital voucher to load more data when i want to recharge data.

Am i the only one who feels that this is ludacris???????????????