Remove charge

I need to remove a charge that I am going to pay, the charge relates to my ex which is attached to the land registry. I have asked my ex's solicitor to complete the DS1 form, but they are not engaging with me.
As I am paying the charge to the solicitors by bank transfer, and have the original documents that state the amount owed, I will have proof that the full amount has been paid.
What forms do I need to complete to arrange for the charge to be removed. 
This is urgent, if not paid soon I may need to return to court.  Please advise what forms I need t complete so that I can have the charge removed.
PS.  I have reached out to over half a dozen solicitors to help with this transaction and all (so far) are informing me that they cannot help, as this matter is too complex.
 

Susan - you need forms DS1, DS2 and ID1/ID3 as appropriate re identity verification
It's easier if the lender (charge holder) completes form DS1/DS2 and submits them along with their identity verification.
Mortgage: cancellation of entries for lenders (DS1) - GOV.UK
Cancel entries relating to a charge: registration (DS2) - GOV.UK
Practice guide 67: evidence of identity - GOV.UK

Thank you Adam,

I have just checked the forms, and I do not know anyone who can validate my ID3 form (going by the list of accepted professionals).  What do you suggest that I do?
 

Susan - you'll need to use form ID1 and a conveyancer instead