If you are not sure whether the other party belongs to Founder Company, ask the other party to mail you a letter of introduction from Founder Company and other relevant information. Anyway, let the other party mail some employees who can prove to be Founder Company before they can talk about rights protection.
If the other party has agreed, you can ask for an interview and let them come to your company for an interview, which shows that you can't talk through some social software.
If you are only complained by the other party, you can remove the infringing Founder font on the page or replace it with a font that can be used for free, and then complain.