as wrote before, i suggested personally to invest in btc and to use electrum because really trustable and safe... so i really feel in fault if he looses 2500 thanks to my suggestion.
don't worry, you didn't lose his bitcoin. It is still there in the address mentioned
it's simply technical problem showing the balance in your wallet.
in addition to saving your seed, you can extract individually that address' private keys just for double safety measure
and do what
TryNinja suggested and also check just in case your wallet is offline mode
@OP, this can't be done in Android electrum (the saving of address' private keys) so it's a pointless task unless you're going to put the wallet on your computer's electrum wallet, in which case, that's sufficient along with writing down the seed as it's unlikely for all three to go missing.