but a better move is to just create a new wallet with proper security precautions, and then send your coins to the new wallet.
He can't obviously do that since he can't even use the wallet properly, particularly can't send bitcoin as per mentioned in the OP.
So, for the time being, try to double check your internet connection, trying clear cached or clear data your browser, or much better use another browser instead, try to use their mobile app, double check if javascript is disabled on your browser.
If nothing happens then you have to use different wallet, you can do that by importing your seed to another, like
electrum which is mentioned above already.