@Waqkas-Ahmed ,
I hope all is well. The only currently available way to block someone who is an INTERNAL MEMBER of the organization other than removing them completely from TEAMS and the A.D. is to use the MUTE setting on the individual user's tile in TEAMS to prevent the notification(s) from being generated to tell you that they are messaging you. IT IS NOT TRULY BLOCKING, JUST BLOCKING/NOT GENERATING NOTIFICATIONS... Microsoft currently DOES NOT have a fully functional blocking solution enabled and available on the platform.
See picture:

Hope that helps...
Cheers,
Adam