You need to speak to the HMRC and tell them you need a new tax code (you should be able to get 1060L if you're not a student) or possibly a different one if you're studying. They should pay it back to you in a future pay packet from work - things have changed recently and you shouldn't have to apply for a rebate at the end of the tax year.
You may still have to pay national insurance though, I'm not too sure.
Best bet is to look at the tax code on your payslip and speak to the HMRC. You'll need your NI number.