Hi just an update. I did a little digging on the net. I found it's down to the texting RTC protocol which is using my supplied number on the sim card. (Even after I've ported my old number over)
My temporary fix was simple. I just swapped the default texting protocol back to MMS and solved.
So i here you ask? Why were some people receiving text from my old number and others from my supplied number? From what I can gather, it's down to what protocol THEY are using. If they use RTC then they see my new (wrong number) if their default is MMS they see my old number(the correct one).
I would like to use the RTC protocol due to the benefits it has. So if anyone has the solution I would be grateful.