Can you use an old sim instead of buying one?

Title says all, for reasons I'm not comfortable disclosing, I cant leave the area I'm in, nor receive mail. I'm very very worried about trying to get a phone number set up ASAP. It's a cricket sim and a cricket phone, and it was on my mom's account at one point. She has since turned it off and won't accept money sent by me to have it turned back on.