This case is rather complex. First of all, you need to properly evaluate if whatever has been achieved is, or not, a work protected by the law on copyright, or if it is simply a mere compilation with very little creation. If the made pages are really simple and anyone could make them without any big efforts, but if mainly they do not have at their basis an inventive idea, without their contents, as they are, they cannot be protected. If, instead, there is something creative at their basis, then they can be automatically protected by the law on copyright. To demonstrate ownership as they are at the moment is not simple, as the work should have been done before, making a contract with the client and depositing the achieved work at the SIAE. Now it could be too late, however the best thing to do is to register, as soon as possible, such work with a deposit even at a Notary, so to be the first certifying ownership. With reference to the client you should do something now by sending a communication bringing to their attention that the rights are yours and inviting the other party to abstain from any unauthorised use. If relationships are good you could talk to the client and evaluate if there is a possibility of undersigning an agreement to simplify the administration of the rights.