I called again and got a much friendlier voice on the other end.
She still wanted physical proof as they don’t have access to the identity check system that the passport office and DLA have!!!!!
She came up with the idea that if my dob was on any of my medical supporting letters then she could use that.
Thankfully my dob was on a lot of letters so she was able to get her line manager to change it there and then.
So it’s all sorted, yaaay.