Esim transfer back to old iphone. I have to return my new iPhonez

[Thesnush]

I need to return my new iPhone and have spent hours trying to transfer the Esim back to my old iPhone. 
Does not want to do this. It’s Boxing Day so ee aren’t open. New phone is being picked up for return tomorrow first thing! Can anyone help me figure this out? All searches so far have been for new phone? I’ve tried doing the transfer but it says status  inactive

[Chris_B]

@Thesnush  Factory reset your old device then just place it next to the new one and transfer everything back.  

[Thesnush]

hi thanks so much for replying, I did try this, in the first instance! after spending 5 hours fiddling and googling It finally managed kinda, still says "can't use last used number to make this call, switch to primary 0000000- instead!' hey ho! I think this is because I was transferring back to an old iPhone 11, not a new phone. This was the issue. Nowhere could I find info re this very specific issue. 

[Chris_B]

@Thesnush  It doesn’t matter if the device is an older model it just needs to be on the same iOS firmware.  Ie 17.2.1 and 17.2.1.