i've been trying to grow some wild plums from seed. They've spent two months in the fridge in a ziplock bag with some perlite and a bit of water, after that i've cracked them and placed the seeds in a wet paper towel. I dunked them beforehand in some water to check if any are viable. they've been now for months at room temp and nothing is sprouting. There were 15 seeds, only three moulded and I removed those, the rest have been in the wet paper towel and haven't shown any signs of moulding or sprouting, they're just not moving anywhere. I even put them on a seedling matt 10 days ago, and still nothing. Any ideas on what's going on / what I might be doing wrong?
I'm not sure what cracking them would do, except possibly damage them.
Your stratification procedure sounds OK, but after that they should have been planted about 3 inches deep in compost in pots, not kept on a paper towel. You could try doing that now, then stop fussing over them (except for keeping the compost damp) and just wait. If they don't germinate within 6 months, you probably killed them with your attempts to be kind.
Bear in mind that trees don't need to be efficient about reproduction. If just one plum germinates from all the plums the tree produces in its entire lifetime, that is enough to make the next generation of trees.