Services unclear and authorisations been pulled back

I have been a long standing clients of theirs and they normally update your policy before next service due and they didn't when I wanted to update the policy they told me I can't I'm over my km's and they can only cover me again for next service but the service they skipped had the campbelt due and now my car is in for service and I phoned and I received authorisation and when the dealer called it was declined and now they say it's a mistake and they can't help me. I have a plan in place for another 4 years but they can't help me? And if my car breaks it's my own problem yet I've had them for more than 6/7 years.