I haven't tried that particular seed, but it sounds like you have a couple of strikes against you before even beginning ;0)

Clothiers: Caltha leptosepala, palustris, and polypetala , Sow at 22ºC (72ºF) in muddy compost for 2-4 wks, move to -5ºC (23ºF) for 4-6 wks, after which temperature should be raised gradually. Sow seed immediately after harvest.

These can be hard conditions for me to mimic indoors. Warm, cold, cool cycle germinators. (so 3 cycles). I'd skip the freeze, and use the refrigerator at its 38F for the second cycle. Even better, I have most success with this type seed sowing late Fall and placing outdoors in my mild climate coastal Z8.

Your second strike is being able to acquire very fresh seed, that can be hard to do buying commercially. With some plants, when they say sow immediately, they mean it. It may not mean the seeds are no longer viable if a little older, but they can take on a dormancy that may take repeated cycles and a couple of years to break if allowed to completely dry out. With those types, I've resorted more than once to buying a plant for my own seed source, then I can sow, grow more to increase the number.

If you still have your seed pots intact, you might begin again with the cycles, start over with the temperatures. Keep them warm, moist for a month. Put them into your refrigerator next though (very few seeds need to actually freeze to break dormancy). Don't rush the cycles, err on the long side. Then given the time of year, once they've had another warm and cold treatment, place them outside in the shade for fluctuating day/night temps, sometimes that can help too.