MOC - Memorandum of Charge, it's a document required to be perfected when the individual document of title to your property has been issued by the relevant land authority
MOT - Memorandum of Transfer, it's the document which will have your name endorsed and registered in the individual document of title to the property. this guarantees your right as the owner of the property. Vital!
Sale and Purchase Agreement stamp duty refers to the nominal stamp duty chargeable. All documents are required to be stamped in order to be admissible in court and more importantly a required documents before your bank will release any monies from your loan.

MOT stamp duty is the stamp duty payable to effect the transfer of the property to you and is calculated in the ratio provided in the stamp act. Generally, the higher the purchase price, the higher the stamp duty.
Sale and Purchase Agreement is not MOT. Sale and Purchase Agreement is the contract between the developer and you indicating the terms and conditions of the purchase. it's the legal binding document giving rise to the purchase.
Stamp duty for Memorandum of Charge is calculated based on your loan amount as well. the formula is X x 0.5%, where X is your loan amount.