1. First instruct the bank not to honour the cheque if they place the cheque for encahsment.
2. If that is done then you will not have to run after them seeking refund of money. So this is most essential.
3. Then send them a written notice cancelling the agreement and informing them not to present the cheque to ban as you have given instructions of ' stop payment' to bank.
4. If they have got the money in the money in the meantime then you will have to seek refund in the cancellation noitce and if they do not then file case before the consumer forum.