You haven't told what controller are you using. Also you should provide the link to the said "datasheet". What I could find was this:

http://rayson-bluetooth.en.gongchang.com/product/1...t/14774507. Is this what you are having?

There is one more rayson at http://www.rayson.com/ but BTM-120 is not there on their product list, so I guess it's not your one.

Are you using correct voltage conversion between 5V/3.3V since most BTMs (bluetooth modules) are 3.3V powered? Do you know the factory default baud rate settings for this module? I recently bought a RN-42 BTM from Rover Networks & had trouble interfacing it to a microcontroller as controller wouldnt interpret it & show garbage (on LCD). To investigate the cause I connected Rx & Tx lines on the BTM as null modem connection so that characters may echo on terminal. The echoeing was okay at 9600 baud. So I got tricked it was "working" on 9600 baud, & kept blaming hardware for many days. But later on I read datasheet more carefully then I got to know the factory default baud was 115200!! Usually there is a pin which forces 9600 baud when pulled high/low.

Of course you will need detailed datasheet. But for now I suggest you try different baud rates.