Did the template your purchased come with any indemnification agreements through which the company that sold it said if any lawsuits were brought against the user or buyer of their programs they would reimburse them for the costs?
A violation of a copyright that has been obtained over an image or other writing, etc. is protected from unauthorized use or promotion. The fact that any unauthorized use may have occured without intent or without knowledge that any wrong was being committed will not remove liability from any party (see here and here for a discussion of this). Also, all parties involved in such action may be liable to the party who owns the copyright individually and, any party who sells an item with a copyright infringement may also be liable to the party who buys it for any harms they suffer.
However, the fact that there was no intent to infringe on anyone's rights may allow there to be a negotiation of what the liability is or should be. Any such discussion should normally include statements regarding a release of all potential claims after the settlement is made so that no further action can occur. These matters are difficult to argue without properly without proper legal representation and it may be best for both you and your client to seek legal help to resolve both of your issues with this company that claims to be the copyright owner. Ownership of the copyright should be properly investigated to see who, in fact, is the proper owner or if it is even owned. An attorney who works in intellectual property, whom you hire in your state, can help you work through this issue and provide you with information to help you avoid it in the future. Although the agreement for the sale form the company you purchased from contained a statement relieving them of liability it is possible, if they in fact claimed full ownership, that their statement of ownership may have been a fraud which may allow you to sue them for liability (but that will depend on state court interpretations).
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