As I said, you can pay the monthly bill with a debit card but you can't transfer £500 to your debit card other than by paying the fees for a cash advance. That would be a 3% (£15) fee for the transaction plus 2.075% per month (about £10 per month). However, you couldn't have a £500 cash advance as that would take you over your limit when the fees get added and this would lead to more fees. If you got a £480 cash advance, the money you'd be wasting would be about £14.40 plus £10.27 per month. The minumum repayment on this card is £5 per month or 1% of the balance but, if you paid this each month, you would not cover the interest charges and you would soon be paying penalties for going over your credit limit.
Basically you could have £480 now and then pay £10.27 each and every month for the rest of your life. If you missed a payment date or went over the limit, there would be penalty charges.
It would not be sensible to use a credit card for anything that you will be unable to pay for in full within the next two or three months.