TL;DR below.

I was raised in a religious family, that was fairly active in the local church. I was active too until the summer of 2016. For the next 2 years, I started resenting the organization, which resulted in me, not attending the masses altogether. It's worth noticing, that I was still "faking" going to the church in fear, that I would make my grandmother and mother angry.
I have a brother that around this time stopped attending the masses and has stopped faking the process. The storm, of course, happened, but around Spring 2020 we were "at peace". In Autumn 2021 I finally stopped faking, stating that I am not willing to participate in any other meeting, that the organization is holding. I was just tired of finding every Sunday a place to stay for an hour, and I am refusing to support the church in any way. The storm happened, with a grand finale, that was Christmas Eve, where my grandmother refused to "break the wafer" with us (old tradition). As you can guess, I have a good relationship neither with my grandmother nor with my mother.
In January 2022, my grandmother had her birthday. She always books mass for everyone in the family (without their consent or notice) for their birthdays, name days, or other important occasions. Besides the masses, we do normal celebrations at home, so we give each other gifts and wish each other the best. We celebrated her birthday early in January and now, at the end of the month, she had her mass booked. My mother came to me on Saturday, stating that "the mass dedicated to my grandmother will happen tomorrow at 12 am". We did not speak, but I took notice of the information. As you may guess, I didn't attend the mass. The next days, my mother is pissed, saying that I should participate. I am currently holding my ground, since I believe, that if I broke once, she would book every mass possible, just to make me go to the church. We are currently not speaking, but I am thinking about what happened, and I would like to hear some stranger's opinion because my friends are saying, that I didn't do anything wrong.

Please, take notice, that I do not speak English, as a first language, so I might sound strange, even though I tried to make the text sound neutral.

TL;DR: I unofficially left the church some time ago. My grandmother booked a mass for her birthday, and I did not attend. My mother is angry for not going. AITA for not going?