First of all, what you need to keep in mind is that the parent who states that there was consent to relocate the child, has to proof that there was indeed consent.
But if you wish to proof that there was no consent, you can use everything that seems relevant to proof this. It could be old e mails or what’s app messages, that show that you did not consent. Or that the move would be temporary. Besides that you could use pictures, contracts, plain tickets or insurence papers. You can also use statements from relatives or others who where aware of the plans. Or statements from employers or schoolmanagement.
In conclusion: you can use just about anything that shows what were the plans for the future.