Tax was deducted automatically through SAGE (if you mean the employer). HMRC are saying enough wasn't paid.Did they take the money or did they overpay you?
He's wrong anyway .Not the best advice I’ve heard today.
Same thing happened to two and a half years back, could have paid them back in one go but opted to pay them back over 3 years.
did you change jobs in this period of time with any type of bonus scheme paid? i did and this caused issues. opted to pay it back over the year through my tax code change
Alex