You don’t need to have a company to apply for the workcation. I am self-employed and I don’t have a business number because that’s how it works from where I am from. But I showed my website, contracts, designations, and income taxes info.
Build a portfolio of what you do and make sure it’s a strong one. Highlight the payments you receive monthly and match that with your taxes. Depending on where you apply, you may not need to show your monthly income. If you think your portfolio is not strong enough, attach a letter of explanation.
Perhaps they selected the wrong clarification requests. I have read that some embassies as for the employers company registration. Maybe upload that and a copy of your ID and a letter of explanation.
This is a classic example of inconsistency among embassies (and Thailand) as I have seen the Arun cooking school name pop up a few times in the past few months with now success DTV holders.