I presume you mean that you don't have your old provider's SIM available and working in order to receive the number porting security text?
In that case you'll need to contact your old provider to see if your number is still available to you and if they can assist with getting it ported it over to 48.
If your current SIM isn’t active and your unable to receive SMS to the number you want to keep, you’ll need to contact your old provider regarding your account. Your current number and SIM need to be active to move to 48.
If you need to contact 48 support about this then see the links in my signature below.
