Legal proceedings should be the very last resort against a bank, basically what PayPal is. Having said that small claims are a pain in the arse to them, so their first line of defence seems to be to hide their UK office, like we don't live here etc. If they don't respond to a court case, the most likely outcome is a ruling in your favour. Hopefully the address is valid enough for bailiffs to gain access to. You say you started "legal proceedings", which I assume is just sending them a letter, and hence the response you had. Only an actual court can set a claim aside, although the other party can ask the judge to do this or strike it, he or she should set a hearing to do this. The preferred way to tack a bank is the Banking Ombudsman. So although their office is in Luxembourg, they still have to answer to the UK Ombudsman and the first approach should be to their relevant officer answering to the Ombudsman. They should treat your complaint a bit more seriously here as they are obliged to pay for the Ombudsman when an issue is raised. Presumably after brexit they will have to use a UK head office more instead of lurking in Luxembourg.