@Annie168
After more thought - I don't even think you should be waiting for your guests to respond...... If you know this because of some mail received or however - and therefore you know the bank in question - get in touch with them immediately to inform them.
Normally to open an account you need some proof of permanent residence - a utility bill, drivers license etc... so HOW did they open a bank account with your address? Either the bank's practices and verifications are slack - or there is something fraudulent happening.
Don't wait - call/contact the bank TODAY.
Best Wishes and do let us know what happens!