I was double-billed
Actually, you were not double billed by EuHost.co.uk. A common cause for being charged twice by Paypal is that customers frequently create a duplicate Paypal Subscription by mistake.
For example when they sign up, they create a subscription. Then the next month, they receive an invoice (which will be automatically paid), and they "pay" it manually which creates a duplicate subscription.
Please keep a check on your active subscriptions from your PayPal account page