6month complaint, arrears and lump sum deduction order

TroubledbyCMS

My partner has had an ongoing complaint with CSA and CMS for years regarding maladministration where he had 2 dependants and 2 PWC (they paying the wrong parent with care and won't seek the money back to address arrears to the correct PwC) and calculations. Nothing has been resolved as yet. No updates. No returned calls but they keep sending letters regarding maintenence but he has no liability  (finally acknowledged by CMS 10 months after a new legal arrangement was granted by the court in Jan 19). Last complaint made in Sept 2019 summarising all of the above again seems to have finally been acknowledged. Arrears are incorrect due to Direct Pay (all proof provided time and time again) yet they froze his accounts in Sept 2019. No update received despite chasing weekly. The MP has even tried to no avail. Has anyone else had to wait this long to A. Have a complaint thoroughly investigated B. Have their account unfrozen and C. Ever Had additional accounts subsequently frozen?
My partner has legal 50:50 shared custody of his daughter so being financially limited impacts the household where there is a minor
Thanks