Particular distributors may have their own notification system for their customers. If your company has such a system then you need to ensure that your company's system is followed.
Otherwise, if the delivery driver deems that the tank may be unsafe they should attach a warning tag or warning label and/or leave a post card with the owner.
The label may recommend to the homeowner that the tank should be replaced and point them to further information so that they can understand why their tank hasn’t been filled, what their responsibilities are as the owner, the problems a leak could cause and how to resolve the issue.
It will also provide contact details for the fuel oil distributor’s own replacement services.