Some people getting my number with Plusnet instead of the ported number

[#1]

Ordered my Plusnet SIM back in September. Received the SIM and then sent through my PAC code from Virgin mobile to port my number over. No issues and everything seems to be ok, my ported number showing up on statement and husband receiving my texts and phone calls no problem. No issues with Whatsapp. 

Now in the last couple of weeks my mum whenever she gets a text from me its not coming up on her phone as me, its coming up as the mobile number on Plusnet SIM i received back in September! 

Why would it be doing this now?

[#2]

I've just switched to Plusnet and like you, kept my number. All fine except texts were showing the plusnet number, then texts wouldn't send at all. Couple of calls to customer services, they decided my sim may be faulty and I've received a new one today. Phoned them to activate it and they said it would take up to 2 hours. My other sim disconnected immediately. I'm now about to go into hour 3 and new sim still not activated so I'm in limbo. Doesn't help that I've read threads on here saying it was taking days.

I'm starting to regret switching to Plusnet already

[#3]

Hi
Would you both be using Iphones?
I have had to fix this issue for relatives who have transferred networks and have Iphones.
See:
https://community.idmobile.co.uk/ask-a-question-18/wrong-number-still-showing-in-messages-after-port...
Regards
Richard