Non refunding of already payed money against buy of plot

I belong to Durgapur, West Bengal. I had taken a plot of land of cost Rs 7.5 lakhs in Durgapur from a developer in their one of their several projects spread across west Bengal, Bihar, Jharkhand. As per agreement for sale of land I had to pay a minimum booking amount and balance amount in interest free monthly instalments in three years and in these three years developer had to develop the plot. As per agreement I can claim the total paid amount after three years with my discretion, even after plot is developed by the developer. in my case, development has been done absolutely nothing. But after claiming they are showing much reluctance, even they are not accepting any letter of customers by post. There are several customers like me, but in the consumer forum I could not see more than 20 claiming refund of money on individual basis in district level consumer forum. Almost nobody could get the refund. As far as we have heard developer has sufficient infrastructure as well as property, but with malicious motive they don't want to refund. I want to ask (1) Whether I along with other customers should go in consumer forum collectively. (2) Whether we should go in the high court. If yes, on individual basis or collectively