They called several times saying they are a private company acting on behalf of HMRC. They wanted to do a security…

Classic HMRC impersonation via vishing — they're after your personal details or payment information. Block that number immediately and report it to Action Fraud; HMRC doesn't cold-call you demanding security verifications.

HMRC will never ring you out of the blue threatening arrest, demanding instant payment, or asking you to pay in gift cards or cryptocurrency. Never. If it claims to be HMRC and it's urgent and threatening, it's a scammer. Hang up. Contact HMRC directly using the number on your most recent letter or at gov.uk/contact-hmrc.