1.You have to send letter highlighting their part of breach of agreement and not completion of project with in committed time, non providing proper service etc., No need to mention cancellation of our side. You have to ask for repayment of you have paid along with interest, damages and compensation.
2. Each and every rupee you have paid is refundable with interest.
3. Negligence and delay is from their part, so you can approach consumer forum for recovery of amount paid and compensation with interest and damages.
4. You have very good chances to get back money. Apart from paying amount through a account payee cheque you must have some receipt and allotment letter you have claim basing on the same documents
5. No need and don't handover any original receipts or allotment letter to builder, any original should be submitted at the time of receiving amount from the builder only. Generally they will refund through cheque, receiving of cheque and submission of originals should be done simultaneously.
6. you will get bank entire amount you have paid along with penalty, interest and compensation. There will be chances of publishing their delay in works or incapability in local news papers which would be damage builder reputation. builder and