Deposits still have ownership.

You still have the ownership of the deposit you paid;

The deposit slip is just one of the proofs.

The certificate of deposit is only one of the evidences to prove this fact. After you lose your deposit slip, as long as you have other evidence to prove the existence of this fact, the school certainly has the obligation to repay it.

argue

Based on this, you can claim that if it still can't be solved, you can sue to the court for settlement.