HMRC has received reports of customers receiving telephone calls where the caller claimed to be from HMRC and asked them for their bank details so a tax refund can be made for a fee. HMRC will never ask you for a fee to provide any services including repayments of tax. If you cannot verify the identity of the caller HMRC recommends that you report it to the police immediately.
HMRC has also received reports of bogus callers who visit people at their own homes offering tax refunds in exchange for a fee. HMRC would never contact you in such a manner and you should report this to the police.