Need help With my snail

Got Valentin yesterday, and since the aquarium shop to home he has been awfully quiet? Like he doenst Even slightly comes off His Shell Even when he Is alone. He didnt eat either apparently??? I was sold a little rock like sand as "great for my fish" and when he finally got active and tried to dig, guess? It got stuck on His Body, I readed that you should remove them as fast as possible to to avoid future damage, so I putted him in separated improvised container and while Trying to remove the rocks that were almost Merging With His Body, a little soft piece of his Shell (Bottom part, near the little "door") now he wont close and now I feel awfull and I dont know what to do to help him. I Heard They need calcium to get better, so I got him All my rocks that visually looks like It has calcium (i dont have vinegar to test. They are clean, It's my rock colection But Even so I washed them again Multiple times without soup before putting them With him) my mom wont let me use eggshells to help him Because according to her "It's too much trouble and he can heal on his own and doenst need Any of that"💀 I tried smelling His (more than once) and he doenst have a bad smell, and he also refuses to eat before and After he got wounded. What am I supossed to do to help him? Is he going to be okay? I'm really worried About him