Try to inform the bank and bank manager immediately after the wrong transaction. Money will get back to your account automatically, if the account number you mentioned does not exists but in case the situation is opposite, you have to take immediate action.
Unfortunately, payments to the wrong account can't simply be reversed, so here's what you need to do for the best chance of getting your money back.
For more information:
PayPal customer support number | PayPal toll-free number