Suspect email
I have received an email stating that my Apple ID has been restricted and offering me a link to go to to restore my service... is this usual or some sort of hoax please?
iPhone 6s, iOS 12
It's a phishing email (accounts don't get 'restricted' ; genuine emails will address you by name ; and presumably it also has grammar and/or spelling errors) - you could forward it to Apple : reportphishing@apple.com , and then delete it.
Phishing and similar emails : Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support
Genuine iTunes emails : Identifying legitimate emails from the iTunes Store - Apple Support