Can a company sue a former employee for contacting the EEOC about that company?

No. The law specifically allows employees to contact the EEOC and forbids retaliating against them. In fact, retailating against an employee or former employee for making an EEOC complaint is a very good way for the company to incur substantial additional liability. The temptation to retaliate is understandable, but must resisted--retaliation in this context is a very bad idea. For more information, you can do to the EEOC's website.