I broke the back pane of glass while drilling for bulkheads

on my new 120
My question is how the H#ll do I get the black ABS top off??
have cut the silicone on each side of the glass... tried tapping the top upwards...
when I was breaking out the glass on the back pane it was harder that heck to get the glass off the top.
Anyone have ant tricks??
Thanks
Dan