Hi adsellars
Many people have been required to prove their identity either at the job centre or in their own homes. You can try and insist that it can be done over the phone, but if you have already tried to do it online and it didn't go through, you will struggle to get them to agree to do it over the telephone. You can argue that under the Equality Act, they ought to make reasonable adjustments for you and allow you to do it over the phone.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
