Do you still get benefits if you are notified about an overpayment?

My dad got a letter the other day saying he was overpayed it was around 18k and saying he was working when he wasn’t he called the social security yesterday and talked them and they told him they are gonna mail him a appeal but for some reason there’s no pending deposit on his direct express the letter and the person he talked to didn’t say anything about him not getting his benefits for this month he is suppose to be paid tomorrow and I am on ssi my pending deposit is already on there but my dad isn’t

I don’t know what’s going on has anyone experienced this any advice would be helpful