AIBU to wish that my grandchildren have an opportunity to see me over the Christmas holiday

Wise grannies, I have written to my sons ex partner to ask if the children would like to meet up with me or phone / Skype me during Christmas holiday. . Predictably I have not had a response. I asked my son to discuss with her and got a lukewarm response about not knowing her availability over Christmas. So my dilemma - do I let this go or just pick up the phone. I will wait until the main days are over incase Mum gets stressy to prevent spoiling Christmas and thought new year a better time as one of my grandchildren has a birthday early Jan as well. I have sent presents and written a personal letter to them but of course no idea if the children will get it. Any suggestions