The only Electrical Safety Supervisory Body is the Register of Electrical Contractors of Ireland (RECI), also known under the brand of Safe Electric. They are prohibited from getting involved in commercial disputes however.
RE: the extractor fans, a Completion Certificate should not have been issued until the installation was actually complete. I'm not sure what you are referring to RE: certificate for heating system, however.
It is not unusual for a plumber/heating installer (e.g. RGI) to install heating controls as these are technically minor works once the REC installs the fused spur for these to connect into. I believe the Commission for Regulation of Utilities (CRU) has confirmed that they believe that an RGI can wire heating controls in place of a REC so long as they don't install the fuse spur. (Unfortunately this isn't deal as plumbers are appalling at electrical wiring and typically commit numerous breaches of the Wiring Rules.)
Have you received a Completion Certificate for the works? If ESB involvement was required this will be a Cert No. 1 but if ESB involvement was not required then it will be a Cert No. 3