Solicitors fees

Hi there im new,just wondering has anyone had any experience similar to my own
I recently received a bill from my solicitor,the bill had increased even though he had given me to total bill a couple of months before,the bill had doubled even though he had done no extra work on my behalf,when i asked for a breakdown of this bill in order to understand the increase he refused,i then asked him to lodge his bill with the taxing masters office,the solicitor informed me if i take him to the office of the taxing master my bill would double again.
can anyone tell me is this legal or simply a threatening letter
thank you for any help given