I'm sorry your family have let you down so often. It's a miserable time of year for that. I saw the Marian Keyes video on Mumsnet a couple of years ago and I think it's helpful in reminding us that despite the supermarket adverts and hallmark films, a lot of people find this time of year a struggle for different reasons
It sounds like you've decided to spend it alone, is that the case? Are you looking for suggestions to meet up with people or to make it special for you?
My thoughts for seeing people:
Ask friends if you could pop by for an hour. You could also ask to join them for the whole day, if you felt comfortable to- but I thought from your OP you were looking for alternatives to that. You could offer to bring a bottle/cake etc over.
Some years I've been for a walk around town on Christmas day in the evening
It's nice to be out with less traffic, with the Christmas lights on and people will often say merry Christmas, which is a nice simple thing to do to feel a bit connected and get out of the house.
Volunteering for Christmas meals might well be full by now (you could check locally). Would volunteering as a marshal at a local parkrun be an option? Or running/ walking it yourself www.parkrun.org.uk/special-events/
Or making it nice for yourself- would you prefer to have Christmassy things or save that for the day your children are with you and do something totally different? Choose your favourite food that you don't get to eat very often because it's not child friendly, have a long bath, watch a film, listen to your favourite album at full volume, do a home pedicure or start a craft project you don't normally get time for.
Those are just my thoughts. Bumping for you in the hope of more ideas- you could also try moving to another topic (Christmas topic? Relationships?) for traffic, although I appreciate that might not be the right place depending how you're feeling.