GetJet is probably doing a wet lease on behalf on Transavia. You won't have any consumer rights.

Some airlines (BA, etc.) are willing to provide refunds / date changes if you don't like the fact that the flight won't be operated by the airline itself.

But to be honest, now that you've added a dodgy OTA into the mix - meaning that Transavia can't touch your ticket - you're flying GetJet or you're buying yourself a ticket on a different airline.