What was the job description of the person who wrote that letter?
I have had letters from FOIs and AWIs who don't know what Day VFR means, don't know what AWK on an maintenance release means, who invent Air Operators Certificates that don't exist and the threaten to audit you because of your bad attitude when you try, in vain, to explain the difference between an Air Operator Certificate holder and a Registered Operator of an aircraft and tell them you don't actually have an AOC; can't even get the right job description for their colleagues, calling people from the FTTE "FOIs" and pretending they have all kinds of powers and knowledge that they simply don't have.
In response to any letter like that I would be straight on to the phone to their team manager, not take much notice of a lowly jobsworth inspector.