[Help!] How to get a phone number that is available under a different carrier

I cancelled my phone number with Mint Mobile while moving abroad in June last year, and it was released. It's currently with T-mobile. I got someone to call the phone number, and it's currently not in service, so I don't have to worry about someone else being in possession of it. I just made a plan with Tello (because I'm abroad), and I'm trying to find a way to port the new number.

I'm wondering if there's any way to get that number back? If I get a T-mobile plan, will they give me back my old number? Is there a way to buy back the number without paying for a full plan?

I need that phone number in order to do my taxes because of two-factor authentication on sites... I didn't realise this would be such a big problem, and I'm soooo stressed.....