[Liesmith]

You can't assume it's not intentional, and we don't have enough info to know if this claim is small or not. Really the only thing to do is to talk to a lawyer. You should already have a lawyer since you've got a contract: talk to them. If you don't have a lawyer, then get one immediately. No one who runs a business should be without legal advice.

[nodata]

At this stage you don't want to threaten your client with a lawsuit until you know the status.

[Liesmith]

Talking to a lawyer is not a step towards a lawsuit, is a step towards knowing your options. You don't have to sue, and in fact unless there is a lot of money involved that's probably the last thing you want to do. But saying "I don't want to sue, therefore I will not talk to a lawyer" is stupid and dangerous. Talk to a lawyer, and tell the lawyer "What are my options? I don't want to sue these people but..." and they will help you chart a course.