As NormanB states, this sounds very much like a warranty issue. That stated, another method is to work through the rear calliper and brake housing, either via the adjustment resetting procedure, or else complete removal of the rear calliper to access the brake pads/piston. Check to make sure that the rear of the brake pad little lug still in situ (never know might have sheared off although unlikely). I can attest that being in China, some of these imported scoots (friends 2006 Tmax, and my AN650K7) are sometimes difficult to source OEM parts for. The OEM rear brake pads for these two model scoots, are plentiful here but they must be for other models, and the ones here do not have the small lug that fits into the brake piston for setting the parking brake etc. These brake pads only cost equivalent of US$2 to buy, whereas the OEM pads are double what one would buy in the USA. As my friend found out, that not having that lug is imperative to operate the parking brake. When he applied the said brake having fit one of the cheap available set of rear pads, he couldn't get the park brake to release since there was no corresponding lug to force the piston apart. Ended up having to dismantle the rear brake calliper to get the hand brake released. I was/am careful to not do the same when I bought and fitted a local rear set of pads, for the same reason. Have since bought an OEM from oneidasuzuki along with other bits and pieces which another friend bought back from a trip back to the States.
Just my 2c worth...