Look, phone company ish liddat one.. if u dun spend above a certain amount a mth, they wun auto give u voucher.. most singaporean just guai guai pay, at most call in and grumble.. but we never assert ourselves.
Tell u wad, if ur contract is at least past 1 year, give M1 a call n say "hi, I'm a loyal customer who's thinking of getting a new phone and extending my contract, so I'd like to request for a recontract voucher."
They won't refuse u.. but if u dun hear from them within 2 weeks, call in again

Sure will get something one. Or at least they will tell u exactly when u can call in again to ask for the voucher.