Hi Ellen - use our contact form to submit the specific details re the property and title number. The paper records will need to be checked to ascertain what, if anything, is held on file re an account number. Not all charges include such specific details when lodged with us but without checking you do not know -
Public guidance: dealing with land and property - GOV.UK
As far as what happens next of the lender won't help is concerned well that all depends on the type of charge it is. For example if it's one where a court can pass judgement on it and dismiss it then that's possible but they are going to need proof of debt and repayment for example so may not be an option
There's still a way to go with this though and it may need escalating with the lender in some way by the executor to try and resolve matters. If they have simply approached them for help but not provided the account number to open the account door, so to speak then they may need to force the door open by escalating matters through the lender's complaints process and more. The need for an account number is a first point of contact and may not always be the last
The house can be unsold forever unless a buyer is willing to complete with the charge remaining in place
You can help press here but this is something only the executor and lender can resolve for you it seems