Refund for over £500 in unused top up balance

[edit_21]

Hi, I have an elderly uncle who has amassed over £500 in unused balance on his O2 sim. I believe it is pay as you go and on autorenewal meaning that every month £10 or £20 is added to the balance. Unfortunately has had a a mental health condition that prevents him from dealing with small stressful situations like contacting customer support and asking for a refund so he has just left it going. He mentioned it to me recently and I thought it was terribly unfair since he has not used the amount and is quite a solitary person so doesn't call for a long time. His phone is an old button bashing blackberry from the 2000s. 

My question is to ask whether a refund is possible for that amount of unused credit. Is it even possible as per terms and conditions of service? How do I go about asking for a refund?  Do I need to prove any medical history from my uncle?

It sounds silly but he actually does have paranoia and is quite solitary and I'm pretty sure someone else set up the auto renewal because they knew he wouldn't know how to top it up manually when he needed. So there is a good chance he probably won't want to send his medical history to O2. 

Bit of an unusual situation so thought I'd clear it up.
Thanks! 

[MI5]

@edit_21 

O2 don't normally refund PAYG credit except if the PAYG is upgraded to a contract. In which case, up to £350 can be transferred as a credit. However, as this is quite a unique case, I'd suggest speaking to O2 to see if there is anything that can be done.

This looks like something you’d need to call O2’s customer service team about – give them a call on 202, 0344 809 0202, or specific payment management number 0800 902 0217 / 0800 032 5302
Also, cancel the auto top up asap.

To stop your auto top-up and delete your details go to www.o2.co.uk/myo2. Then go to auto top-up and you can then cancel your auto top-up and details.

https://autotopup.o2.co.uk/o2uk/FAQ.aspx