This number also called and left a message to say my son was going to be arrested for tax fraud. He left his name as Robert Marshall.

Accent and phrasing sounded suspiciously American. Definitely some kind of spam number.

This person phoned (David), saying that he was calling from the tax office and I was going to be arrested for fraud. They were going to take legal action against me. I told him I would wait for them to come and arrest me as I am an honest person and have not done anything wrong.
This is a scam of sorts and when I asked for his last name so I could call him back if he had any questions, he said I could ask him now, but he wouldn't give me his last name. I then told him I was going to hang up and he told me not to believe everything I hear about it being a "joke".