I knew how it feels to be "robbed unknowingly" . You can call 211, choose the option for PREPAID. They can check and validate your concern. They can process adjustment if your complain is found valid..
Try to call the prepaid hotline, 211 or access the free chat support by texting HELP and send it to 1234. I'm sure that your load will be credited back to you.
BTW. Prepaid hotline is open only from 8 AM to 10 PM