Overcharged account balance.

The prepaid balance is not refundable.  You are paying for service, whether you use it or not, so USE IT.  

Change to a monthly unlimited talk and text and make minimum deposit to keep balance rollling over.

The only reason for your balance to continue growing is you keep adding to it, so stop adding to it. Just make sure you keep track of your expiration date. If you let the balance expire, it is gone.

From your other thread, it sounds like you have a $25 refill set up on autopay. Autopay on a "pay per use" plan refills $25 every 90 days, not when your balance gets low. A $25 refill expires in 90 days, so if you just stop refilling, your entire balance would expire in 90 days. You might want to educate yourself about expiration dates. 

Read section 4 on expirations 

https://www.att.com/legal/terms.prepaidPlanTerms.html

Plans

https://www.att.com/prepaid/plans.html