I was going to suggest you hand pollinate but you did that, I don't grow these melon's so cant tell the different flowers BUT do they have male /female flowers and if so, are you sure you used the right sex ha, ha, ha, well I'm trying.
Have you perhaps overfed the plants and they have went mad making flowers and not needed to set seed fruit.
Maybe IF you could send us a picture someone could see a problem that is not evident to people who dont grow these plants.
Sorry but with I could help further, hope someone else can come in to advice you.
Good luck. WeeNel.