Threatened with Garnish for an Account that is not mine.

I received a Letter of Demand to pay for tax of a company I did not own but only worked in. I have been receiveing calls and SMS's regarding this matter and tried to resolved it by emailing and calling to explain my situation. However after confirmation that I will be removed from their system I get another email from their consultant who was rude instisting that the Garnish is in place. I'm unsure if I will even get help for this query but I am very annoyed and irritated. If anyone knows how I can resolve this matter please advise, I doubt I will get any help from the company on this matter.