If you really don't want the interview then call the school. Be professional and politely give them your reason for not wanting to attend.
Ex:
YOU: Hi my name is ____. I've received an interview for the school and would now like to decline the offer. Is there someone I can talk to this about?
Them: Yes, I will transfer you to "
so and so" right now.
YOU: Thank you
Them: Please Hold
THem #2: Hi how can I help you
YOU: My name is ____. I received an interview and in the time since I have been offered 12 other interviews at schools that I feel fit me better. If it is possible, I would like to cancel my interview with this school.
Them #2: Ok, what was your name again?
YoU: _________.
Them #2: Alright, thank you for your notification. We wish you luck in the application process.
I thought that sound pretty good
Just be professional about the situation and make sure you have an
armful of other interviews before you do this because you don't want to get to the end of the cycle and not have any acceptances