Was I correct in maintaining 2800 before the IAF or is the
controller allowed to clear me below a minimum dictated by an approach
chart?


I often fly this same approach. On occasion, a controller will give
me a lower altitude than published, but when I say, "Skyhawk 1234X
requests 2800 to comply with the procedure", they always give it to
me.

Your controller made a mistake and you should have corrected it. His
instruction to descend and maintain 2,100 was an order, and
technically you were wrong to ignore it.

BTW, MVA in that area is probably 2,000 feet, so you were safe at
2,100, but not in compliance with the procedure.

Controllers make mistakes like this *all the time*, and you should be
spring-loaded to deal with it in a polite way.