Managing personal Outlook.com account settings, security, and privacy
@Heather Orsanic said
Not only are the rules not working but now I've apparently reached the maximum amount of blocked senders I can have.
Blocking the Sender or putting Rules in place will not stop Group Joins and the Calendar Events they generate.
I'm being added to 50+ unwanted groups
I am sorry that you got targeted with this kind of Spam attack, and while it won't help fix your immediate problem, I suggest that you Vote for this Feature Request. If enough people complain maybe Microsoft will give us an option to stop Spam Group Joins.
Add an option to block being added to Outlook Groups without consent
https://feedbackportal.microsoft.com/feedback/idea/a17de24f-8ce6-f011-92b9-7c1e5244b89c
(You must "Sign In" at the top right of the Feedback page before you can vote).