Mr. Haas has opted out, so I will be offering my input on your questions.
As you already know, covenants not to compete are unenforceable in California. The "radius" doesn't make a difference. The exception is if there is a sale of a business, which did not happen here.
Furthermore, for an "Cease and Desist" order to be valid and enforceable, it needs to be issued by a Judge, not an attorney or certainly not your former employer.
In addition, your former employer can't impose a "fine" of anything; fines are criminal in nature, not civil.
I don't know if your employer's headquarters is someplace else than California; covenants not to compete are valid in most other states, and "radius" is an issue.
A strongly worded letter from an attorney (with a mention of malicious prosecution if your former employer tries to sue) should knock the nonsense off.