In the UK we have the Financial Conduct Authority. For a registered financial institution you have protection of, I think, something like £80,000 in case the bank goes bust and you can also ask them to investigate any complaint.

I have done this once for my own account and a couple of times for others. They really do look into every detail and will award compensation if it's clear the bank was at fault.

Institutions that don't have this protection include Trasferwise and Revolut, both of which I have had issues with in the past.