Changing nationality on Zairyu card

Am trying to change my nationality from country A to country B on my Zairyu. Both foreign nationalities, and when I rang immigration on two separate occasions, they had both said it’s a simple process of going into the office and bring along both passports, and they will issue a new card.

However when I went in person, immigration wouldn’t do it and wanted proof of renouncing one nationality before switching to the other. And once that is done, to come back into Japan to update the Zairyu card. I’m definitely not keen to do so and separately, I questioned how would I then reenter Japan with country B if my Zairyu card states country A which I have just renounced hence no longer having a valid passport. The lady at the counter said let the immigration officer at the time know - this I do not buy and just seems risky!

Had anyone tried to do so with a different outcome?