Barclays 0% apr monthly repayments in UK on iPhone 12

This would be my first time using a finance option from Apple. I've been told on a call by Apple sales that I can pay off the phone early and that I can alter the amounts I'd like to repay. I just want to see it in small print before I make the commitment so that there's no misunderstanding.

I have asked Apple to clarify how I make these changes, and to confirm that I wouldn't be charged a penalty when I repay early. As it's a 0% loan, this makes sense obviously!

But, Apple could not confirm and told me to ask Barclays (the financing partner) which I have just done.

On a call, Barclays said I would need to ask Apple. I was told I "wouldn't usually have an early repayment fee".... but the gentleman I spoke to couldn't say for definite.

My questions:

1. How do I alter the amount I repay monthly?
2. How often can I make that alteration?
3. Will I be charged an early repayment penalty?

I found it alarming, that Apple can't answer me and told me to contact Barclays.... and Barclays can't answer me and told me to contact Apple..... ??

Thanks in advance all