Thank you for your question. Please permit me to assist you with your concerns.It is indeed possible to sue based on an 'in use' copyright. Since your product has been in the domain longer and potentially acquired 'secondary meaning', their app name, being 'substantially similar' can be shown to be infringing upon your property rights. So yes, you can sue for potential damages, and you can file for an injunction demanding that the sale of their product be stayed until it substantially changes from yours and the name of the product changes also.Good luck.
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