I am a little confused. Where does 'my number' enter into it and what is your number?
What I understand is that you have ported 123-123-1234 to ring central. A caller (assume 123-123-1235) then dials the 1234 number whereupon ring central then sends to your 3CX instance. Contained within that call is not only the information that allows the 123-123-1234 to be identified, but also the originating caller information - maybe, maybe not.
Some SIP providers may charge for the passing in and out of caller-Id info (CNAM and/or CNUM). I am of the opinion that in most cases, if the number is there, the SIP provider will pass it through. I think it more traditional that if a charge is to occur, it will most likely come about trying to attach a name to the caller-ID number as they may need to dip into a database to attach a name.
The 3CX log file should be able to reflect what it saw as the call details which would indicate if the message contained the desired info. Of course, you could also try and use a known landline phone and possibly even outside of 3CX, ring central just to confirm that the originating caller phone & carrier is sending the callerID info. Then do the same using the same phone and carrier calling through ring central to 3CX.
MIXIG gave you the method by which the 3CX system will examine the call, determine if it is the DID of interest (1234) and then send the call to the destination as stated in the rules for this particular call and it will append the inbound rule name (as he has input "NUMBER A") to the display of the phone...if that is where the call is routed. "NUMBER A" can be any label you wish to apply as it is used merely as an identifier to help you discern either who is calling or at least which number was originally dialed to get to you at that extension. Use the same setup for the second DID line using the appropriate DID mask and a different inbound rule name.