I guess the three months in a warm spot was good. That will have broken the first dormancy of the roots. But these roots will normally only start growing at intermediate temperatures, thus somewhere 10-15°C, not at low temperatures in the refrigerator. At intermediate temperature, which is lower than the ‘warm spot’ they will grow rapidly in a few weeks time. When they are several cm long, you can then place them into a cold spot for some months to break second dormance so that the plumule will appear when you place them in a warm spot again. From what you’ve written I deduct that you’ve gone straight from warm to cold without the intermediate temperature. When the roots are not yet there or are too small, the first leaf (plumule) will not appear when placed in a warm spot again. Some seeds have developed their first roots you say. If they are long enough (minimum 2 cm), you can now place them in cold again to break dormancy. After this those will grow when placed in a warm spot again. The others are best placed in a spot with intermediate temperatures for the roots to appear after which you can give the cold temperature again and then move them to the heat. Alternatively if you leave them outside, they will simply receive warmer temperatures, in Fall they’ll develop their roots and after Winter they’ll grow. At least that’s my experience, but species differ in their precise requirements and after many years I still have rather variable results myself. Good luck!