How do I remove a charging order on my house

in 2012 I had a appilcation for a second charge on my prorety granted. I have since paid the amount owed to the compnay and have numerous letters and statements confiming that my balance with them is ZERO.
The problem I have is a dispute with the Solictor involved. They added interets which I fully expected, I have since asked how much is outstanding, they have replied with 3 different figures and have refused to send me detials of how they have calculated the outstanding and now we have a stand off. I am willing to pay, they can't prove the correct amount. I have reported this to the Finalcial and Legal Ombudsman and resntly to the SRA Solictors Regulatory Authority. 
I want sell my house, this outstanding charge is stopping this mainly because no one really knows how much is outstanding.
Can I appeal, I have spoken to the Compnay I owed money to, they simply send me satements showing nothing and refer me back to their Solictor who doesn't answer emails, promises to return calls and doesn't
How do I proceed?

Richard - how is the charging order registered please? Is it protected as a restriction in the B Proprietorship Register or is it a noted charge ion the C Charges Register?
I'm assuming it's a noted charge as you refer to a 'second charge' and if so then you can apply to cancel it using form CN1 plus supporting evidence to show that the order has either been paid off or dismissed by the court