Money owed from CSA

I've been informed by the CSA that I shouldn't have been paying maintenance since September 2015 when child benefit stopped. I have given them my bank details so they can refund the money but they have told me they need to investigate the file from the start (Sept 2010). I've not missed any payments. They've now told me it could take 4 weeks or more while they look into it again. They also took a payment from my salary after being informed payments have stopped but they still refuse to refund the money until everything has been looked into again.


I just need to know how long a Company can keep your money for before refunding it and continually telling me they are looking into it sorry, "reviewing" it.


Just would like to know our next step steps in retrieving my money.