I believe that all of the possibles you were told are incorrect.
That fish appears to be a Himantura Krempfi also known as the Asian Tiger Stingray.
H. alcockii does not have the pronounced sharp nose it is rounder and they lack markings on the tail. Colorartion is dark olive-brown with numerous small light dots.
H. bleekeri has a brown underbelly with a white elongated white spot in the center of the belly.
H. draco is brown with a light colored disc edge that contains dark spots.
H oxyrhynchus in my opinion is the most beautiful of the Himanturas and is most similar to the ray you pictured but has a tail nearly 4-5 times the disc length, so if this fish has a tail that is extremely long it's possible it's an Oxy.
As far as H. uranak goes, the honey-combing/leopard spotting just isn't there. Even in the juvenile stages these fish maintain the same striking coloration as the adult.
Again, strictly from the photo posted I'd go with H krempfi. This fish grows to about 40cm (DW) comes from the Phraya and Mekong basins and should be kept in brackish water.