Getting existing number transferred to new sim, can’t get a pac due to 3G switchoff

[Dp707]

I need to keep an old 3 number, how do I transfer this to a sim I’ve purchased that has a new 3 number.

[PeteG]

Hello there. 

A number can't be transferred directly between accounts. You will need to port the number out to another network on Pay As You Go, then port the number back onto your new SIM.

I'm unsure why the number would be saying it doesn't exist, where is it that you're seeing that message? 

Pete.

[Dp707]

It’s a new sim in a new to me phone, as the old phone has stopped working due to the 3G switch off, can’t simply move the sim over as it’s the old large size. I tried the helpline but it’s saying the old number doesn’t exist even though I used it in Crete last month