How to cancel my new Three SIM only plan and stop my number being ported from old provider

explorerm

I successfully applied for a 12 month sim only plan with Three on Thursday. As part of the sign up I provided my PAC code to port my number from O2. I want to stop the number being ported over and cancel the SIM only. 
Reason is I misunderstood when my O2 contract ended (I thought it was 30 June but its 31 July). I've been offered an upgrade to a SIM only from 30 June with O2.
I tried to call Three today but with very little success. 
I was told to insert the new Three sim (when I receive it tomorrow morning) and call Three to cancel and get a new PAC. 
Help! It's important that I dont lose the O2 number.

eDicky

When exactly did you provide the PAC to Three? It may have already been applied and be too late to cancel, in which case the advice (presumably from your call to Three) to activate the SIM and then cancel and port your number back again is the only way to go.

Otherwise, if there's still time you can try to halt the PAC being applied, I think I've seen the option mentioned on the O2 website.

explorerm

eDicky said:

When exactly did you provide the PAC to Three? It may have already been applied and be too late to cancel, in which case the advice (presumably from your call to Three) to activate the SIM and then cancel and port your number back again is the only way to go.

Otherwise, if there's still time you can try to halt the PAC being applied, I think I've seen the option mentioned on the O2 website.

I provided the PAC code to Three on 25th June the same time as I applied for their SIM, all done on Three website. It allowed me to specify 30th June for the transfer of my number (to Three). 

Think I might try calling Three again today (I called them yesterday). Do you think its worth going to the Three shop? Will also call back O2 as perhaps it's possible to cancel the PAC code and then when Three try it tomorrow it wont work ? 
 

eDicky

Beware of being badly advised by Three personnel in their call centre and in shop. Judging by the way you have explained the situation here, it should be clear already with them, and what they already advised you sounds reasonable.

Maybe you can have the PAC process cancelled at the O2 end, if you call them or via website, as it sounds like the process is still pending today.