Thank you for your mail I am sorry to hear of the difficulties you have experienced with the WebFiling service. There have been intermittent issues for some of our customers when using the new WebFiling service. Our IT side are investigating to find the cause and will endeavour to resolve these issues as soon as possible.
As a temporary measure, please visit: Sign in to WebFiling - Companies House WebFiling account - GOV.UK (company-information.service.gov.uk)
Select the option to file a mortgage charge. This should take you to the old WebFiling sign in screen.
The above response has just been received from Companies House, in which they acknowledge the difficulties which some individuals have experienced.