As far as I understand your biggest fear is to lose this burner number for verification purposes (ie, korgs).

Try asking or googling if this number you used could be ported elsewhere that offers such a service.

Also - just in case - might be a good idea to get another temp burner (maybe via software burner apps) and let all korgs know from your old number that you're switching to a new one and provide that new one. That way you won't lose your standing in case you won't be able to port the old number or it doesn't go seamlessly.

Good luck!

Have you tried buying a monthly plan online?
My trackfone allows me to access my account via an app and i can reload one or more months at a time. I use a Visa gift card for the transaction.  

 
If all else fails, and before your minutes run out, let your favorite providers know you'll be switching phone numbers soon so it's easier to maintain your network.

My Tracfone number is on its 7th handset now (Samsung A11), and is not on a "Plan" other than getting reloaded from cards (purchased with cash) every 90 days.  I think you can still buy Tracfone-packaged devices and activate them privately.  I'm not using their "Smartphone" cards but the older type.  At some point I got on a Triple Minutes for Life bonus, so I have way more minutes/megabytes than I'll ever use up -- I only renew to extend the service time.

as much as possible . . . .

 
BEFORE you run out of minutes, get the Tracfone others are recommending you your remaining minutes on the expiring phone to text your new number to all of you providers and agency bookers.  This will make it smooth transition to another number.  If you let it run out before doing this, it may be much more difficult to get everyone to accept the new number as still being you.  If you text them out of the blue with a new number, it can look like some new guy trying to piggy back on your reputation and history.  

Get a Tracfone and buy the one year of service card with cash at Walmart . A few years ago it was around $300 now its more like $100 and change. Also be aware that Tracfone  was sold to Verizon in the last year or so. As soon as I heard the news I bought (two)  one year service cards to carry me through the transition.