I'm sorry to hear that you're dealing with this particular situation.

Unfortunately, there's not a way to disable the "missed call" notification on the phone that I was able to find. You might see if it's possible with your carrier to stop sending the "missed call" signal for calls coming from a specific number, but you'd have to ask your carrier. Unfortunately, the phone doesn't have an internal block for missed call alerts, unless I believe, you turn them all off.

Does that help?