Medical expense is a non-refundable credit, like almost all tax credits today.
This means that the credit of tax reduces your tax payable. When your combined amount of non-refundable credit exceeds the amount of tax payable, no further credit applies.
Also, Medical has a 3% deductible, in your case around $690, so you have the rest ( ~$700) available to claim. But it is a non-refundable credit (Not a deduction).
A refund is only,ever, when you overpay tax on your income. This usually happens when more tax than required is taken off your pay at source. Refunds are not new money!