The key to no contact is to make it look like you're getting on with your life.
Just refusing to answer the phone because you're not wanting to answer her calls, especially if she gets that impression, just leads to pissing her off.
You've been upbeat around her, that's good. And probably why she asks you to stay for dinner.
No contact is not a punishment on her. It's an opportunity for you to unplug from the drama that keeps you messed up inside. If you're not answering your phone, have a good reason why. Don't sell this as though "I'm cutting you off!" Sell it as "Sorry darling, I was out with Larry and Mo doing a little golfing and didn't realize you had called." When you do speak to her, you should be upbeat and positive, kind and friendly. No realtionship talks, no questions about you and her and your marriage.
Get it?
Blessings,
Bill
"Don't tell me the sky is the limit when there are footprints on the moon."