Sixto is likely correct with the pads hanging on the lip of the rotor. You will have a hell of a time to pull the pads without the proper puller, if they have been in there that long.

Try and use a prybar to force the pistons back into their bores and provide some additional room for the pads. You only need about 1/16" per side. Then the pads will move outward far enough to clear the lip of the rotor.

I had the same issue with the SDL last month.