Sim swap problem - am I using the right SIM

[JMS65]

I am on a pay monthly tarrif with a very old Samsung phone.  I was recently given a Huawei phone and wanted to swap my sim from old phone to new.  However new phone takes a different size of sim so I have got a PAYG sim for the new phone but when I try a sim swap it is not recognising the serial number of the new sim.  I therefore filled out the online form to swap my number but I am now concerned by the wording as it says "the new sim will stop working" when the number is transferred. Nothing has happened yet and my old sim is still working Will I lose both numbers? Will they be able to do it considering it is a PAYG sim that came with the phone and im on a monthly contract? I have tried all avenues for contacting 02 without success and there are no shops I can go into.  I can't find any email address to contact them either, so am hoping someone will be able to help me - i'm not very tech minded and have not done this before, so sorry if the questions seems a bit dumb! 

[Cleoriff · Accepted solution]

@JMS65 

PAYG and Contract sims are different.

I would  contact O2 on any of the numbers in this guide. Guide: Coronavirus Community Help and Support 

0800 587 4005 is the best number to call.

[JMS65]

This is brilliant - was actually able to speak to someone and get this sorted.  Thank you so much.

[Cleoriff]

Great news @JMS65