Changing phone numbers

[TariTime]

So I recently bought an S20 through tesco mobile and asked them to swap my old phone number from giffgaff to tesco, (I've had the number for 12 years, I wasn't about to give it up now!)

Tesco have said that they have transferred  everything across but the number on the phone is still showing the tesco number, not the giffgaff one, meaning  the phone is not receiving any messages.

I can send from the giffgaff number, but replies are going to the original  giff gaff sim. 

Tesco online help are rude and unhelpful. Pls help.

[Richmar83]

Are you saying that messages are sent from your handset using the Tesco SIM using your existing (12yr old number) but any incoming messages are not being received on the Tesco SIM but rather they are going to the GiffGaff SIM? Can you make calls and receive calls to your old number with the Tesco SIM in the handset?

There's no settings within the handset that changing would assist. The SIM card is what deals with the connection to the network and this uses a unique ID number which authenticates you on their network and the linked telephone number. If you can make and receive calls on your previous number and send messages from it (with the Tesco SIM in the device) then they've ported your number successfully. Your number cannot be linked to 2 SIM cards at the same time as when it's ported over then it's removed from the originating network (if you put the GiffGaff SIM into an handset it should not register on the network)
All I can suggest is to reboot your handset with the Tesco SIM in and then see if it forces a network refresh. Other than that then you'll need to speak to Tesco and see if they can re-register your number against your SIM ICCID and re-establish it on their network. Both GiffGaff and Tesco use O2 infrastructure so it's just a matter of making sure Tesco have moved your number fully onto their 'listing'