[Q] Text Messages Going to the wrong Person. Help?

[osskhan]

I have a Galaxy S3 with firmware 4.1.1 stock.
Here is the problem.

I have 2 people having same mobile numbers but with different carrier so different code.
When I SMS to either one, the Thread gets merged and I can not differentiate the 2 numbers. How can I make 2 different SMS threads work simultaneously?