Top up Contract airtime expires

I had an query about the fact that I pay monthly for my top up contract so airtime accumulates if not used what will happen regarding my airtime, I was simply told not to cancel or down grade as I will lose my airtime.<br> <br> I was now twice advised that if I either go on a less expensive package or choose to go prepaid and not renew due to affordability they will CLEAR my airtime technically take it away.<br> <br> How is legal after paying every month for your contract its like buying airtime anyway and just buy a phone prepaid.<br> <br> I will seek further advice regarding this as I feel it is not acceptable after paying every month for something they can just take it away as you can afford to keep your contract going.<br> <br> I feel I paid for it why should they take it away its like throwing money in the water it just does not make sense why take out a contract then in the first place?<br> <br>