ARE YOU SURE you want the same electrician??? He has messed up the original cu change, probably falsified the certificate (you did get one??) left you with a dangerous install and had the cheek to charge you for it.
Get him back to rectify his mistakes, check he is registered at www.competentperson.co.uk if not report him then engage another sparks to do any further works and check over the cu install
The company is registered.