Man, I was having the toughest luck with clones, too. Honestly, I think if you are having a tough time, then chances are there is something in the environment keeping them from taking root.
I was having the same problem as you, they would just sit there until they sucked all the energy out of the leaves.
If they have been sitting there that long and still don't have roots, then chances are they aren't going to make it.
Is the equipment you used to cut them sterile ? You really shouldn't be having to soak the cubes in clonex twice. What, are you using vlonex powder? Does it mix into a gel? Did you not try soaking the bottoms of the cuttings in the clonex, instead of the pellets?
For me, I watched my keepers get passed on, one after the other until I got an aerocloner. If you are that serious about getting the clones to work this time, then I suggest checking out the diy section or YouTube and building one, they are super easy to make for like $30 or less including the fountain pump.
Btw, a reptile/seedling heating pad under the tray would probably really help out. I have a regular (like for your back) heating pad hooked up to a timer, so it only ran every other hour bc those get a lot hotter.
