I hope you are well. I saw the report this morning and unfortunately I cannot help you as this is way above my scope. This has to do with our legal team as infringement on intellectual property is a legal matter and can potentially be punishable by law. I do know however that it will be extremely difficult to recuperate this Instagram account, especially considering that the team issued warnings before shutting it down.
You can try reaching out to the legal team, but at this point I would advise you to create a new account and manage it directly for your client.
I know your agency is professional and works accordingly, however there was still an infringement from the client’s part. I’m sorry I could not be of more help.