Flat allocation

Hi I have booked a flat 3 yrs back . I have paid 35% of the flat amount. The flat is not yet ready and builder says it will take 2 more years to get ready. Today we went to get whole details on allocation and loan process . They said our allocation is cancelled and already booked to someone else . Now what should I do. Flat rate has doubled in this 3 yrs and for same size flat I have to pay two times the amount of this flat now. They said we have send the communication to your agent and you also never came to ask in last 1 Yr so we cancelled the flat. What can I do can I go to consumer forum or should I do a civil case??