I would try this ...
http://www.gemoney.co.uk/en/utility/contact_list.html
Select the relevant address from the list.
In your e-mail explain that you have been unable to obtain information from the call centre as there seems to be a lack of understanding on the part of the call center.
Do NOT quote your account number in the e-mail. In your e-mail,I would ask them to provide you with a contact number of a person in the UK who will be able to assist with your enquiry.
If they are unable to do this then Your IP should have the common sense to suggest that you provide an estimate of the amount that is due to GE and note in the proposal that it is estimated. The process cannot become protracted due to one creditors inability to provide you with, what at the end of the day, is a very simple piece of information.
If you continue to struggle, provide a written authority for your IP to contact GE. Ask them to obtain the balance on your behalf.
Tell it like it is.
Tell it like it is.