Information 'not recognised' when trying to create an account online

I’m trying to create an online account (for my octogenarian parents). 

I’m asked to enter:- first name, surname, post code, DOB and OVO account number.  All of which I have.

But after entering the information, I’m getting an error message saying:-

“Oops, there’s a problem… Sorry! Some of your details don’t match your account information. Please check and try again. If that still doesn't work,give us a call.”

So I tried again, several times to no avail, so then called them. 

The automated voice prompts me to enter the same information, then I get the same response, (ie, that the information doesn’t match) and it says it will transfer to through to someone that can help (or words to that effect).  The automated voice then says there’s no one to take my call and asks me to leave a voicemail (which I did).  

I also tried the live chat option.  Which after a while says it will put me through to someone that can help.  Then it immediately returned a message saying:-

“We're really sorry but Live chat is currently closed”.

Does anyone know a method of contacting OVO that actually works?  I don’t live with my parents these days, so can only help out with their admin stuff at certain times.  And if OVO call back from the voicemail I’ve left, my parents will struggle to follow any instructions they’re given as theyre not technical at all, and as they both have issues with their eyesight, using their small mobile screens would also be a major barrier for them.  Any idea would be gratefully received.

Many thanks and kind regards,  

Lesley