Builder not developed plot

Dear Sir/Madam, I need help on the below situation. I booked a plot kolkata giving around 5.5 lakh and a sale agreement is executed in 2012 Decemer. After that every month I have given some money and total given till date is 13.5 lakh. They were supposed to develop the plot (it was supposed to be township) but till now they didn't do anything. Now they are asking to register plot and don't want to return money with interest of national bank which is mentioned in sale agreement. What should I do now? If I go to consumer forum. how much time approximately it can take and expenditure I can incure.