Of course the Captain is ultimately responsible for everything and everybody on board the aircraft. However, when he/she signs the NOTAC, he/she is acknowledging that information has been received regarding type of DG, quantity of DG and where it is loaded on the aircraft. The captain's responsibility can only go so far. The acceptance staff will have signed an acceptance check list and they have fullresponsibility for accepting the DG as suitable for transport by air.
It would be interesting to ask your two authorities to indicate the legal document and/or ICAO Annexe material upon which they base their adamant claim.
With best regards
DC8rider.