You are responsible, & they can make you pay for the services. Your best bet is to set up a payment plan, & make smaller monthly payments & attempt to pay the debt. They may write off a portion of the debt.

US private health insurance would pay for our stay @ a UK facility for urgent or emergent care. If you only purchased travel insurance, & have no actual private, non-travel medical insurance you are liable… I would start trying to force the insurance plan to pay.