IMO, If affUtd close someones account due to allegations of content theft (which I don’t doubt actually happened..), they can get sued / lose face / lose an affiliate unjustly. you have no proof that the content is yours originally, and they cannot be judge and jury. Imo contact the thiefs ISP and get the site taken down.. The ISP is probably liable for hosting copywritten material.
Therefore I agree with them telling you to seek legal advice or try to deal with it yourself (much as it sucks)
good luck