Please do not respond to an email from the tax office that asks you to complete a form to get a tax refund for over payment.
It is a hoax mail. It looks very real and HMRC are aware of it. My husband was caught out yesterday. He has his faults but he is not stupid and he was hoaxed.
Email address on mail is HMRC.co.uk
HMRC would never send this sort of thing by email.