I'm surprised no one mentioned tapping the filter on the circumferential lip using a cold chisel to try unscrewing the filter. I've never tried it, but it seems like a good last resort (assuming there's enough clearance).
xlt4me, I ran into the same surprise with my Wix filters. When I switched from Mobil 1, Motorcraft, or other OEM where the standard cap wrench fit, I couldn't use the cap wrench for the Wix! It's a shame that the Wix manufacturers overlooked this feature on an otherwise fine filter.