Hey there,
I would have advised you to send it to them to Apple to check. Without Apple having looked at it they will not be able to check your device and proceed from there.
Now that you have sent the phone to Vodaphone, they will pick up being the original seller. Hopefully Vodafone will help you out with your problem swiftly.
mind you that you can’t have Vodaphone and Apple check your phone at the same time. One or the other party is going to let the other finish your request.
Since you asked Vodaphone to look at it you can ask for a full refund considering they have sold you a product that has not lived up to your expectations and by European regulation you are eligible to get your money back.
what you want to do is be clear on who you’re requesting service from. When you ask Apple, follow their procedure. When you ask Vodaphone you have the advantage of them being your direct supplier and the regulation should help you out.
hopefully this will help you out.
PS
I know it’s annoying but patience is key