Refusal for the replacement

I bought house and lot in one of subdivision and have already the contract which indicate the specific unit. However, the developer emailed me that theres some alteration with the lot in which my unit has been affected and need to replace. Please help me to make a rejection letter for the proposed unit that their offering as i dont want the new location . And as not following as what in the contract i want to request for the refund of all the payments including the downpayment.