[TRE Cup]

As you have mentioned that both upper and lower c -clips were removed, it looks like corrosion set in enough to rust weld the pin to the brackets. Since the plastic flipper is being replaced anyway, you can remove the pin by a) break out the plastic between the upper and lower brackets b) using a vise grip set of needle nose pliers, clamp on firmly to the pin and rotate it back and forth to break it free. Careful on how much pressure you put on the pliers as you can create ridges that won't pass thru the hole in the lower bracket!