It's always disappointing to hear of people having bad experiences in TK J, I flew exactly the same flight from IST-BKK back in March and loved it - whilst not particularly forthcoming with more drinks, I didn't feel that if I'd asked I would have denied service.
I've got SIN-MAD and LHR-HKG coming up in TK J again so I'm hoping that the service stays consistent with what I've experienced!