Am sure the below is the case,
All you needed to do is to do a "Sim Swap" without topping up as you've just made another account up with a different number etc so you can't get your old number back this way, the only was to do this, is to sign in to that account you want to keep the number for, order a sim and then do a "Sim Swap"
Here's a little help,
Before Doing A Sim Swap >>
Backup / Copy your contacts/phone numbers from the old sim to your phone or write them down, otherwise you will lose any contacts from the old sim as soon as you do the "Sim Swap"
- Make sure you are signed in to the account you want to keep the correct number etc.
If you don't have a spare SIM card , Order Here >
Its up to you if you want to keep the new sim alive and just use that for a month what you've just activated or give it to a family member or a friend.