Just my very brief view of this current development........
1. If the equipment had presented a health and safety risk......
It would have been dealt with quicker than this.
2. If the equipment contained sensitive or even classified data.....
It would have been dealt with quicker than this and likely the nature of the issue kept from the new owner to reduce the risk of downloading, copying or dissemination.
3. If someone is in the POO for incorrectly processing equipment that was meant to be destroyed according to a contractual obligation........
Such matters end up taking time to sort out as there will be meetings, discussions between involved parties, more meetings and eventually a decision on the way forwards to correct the situation in a satisfactory manner. Such decisions can involve a significant amount of money, lawyers, managers and time wasting !
I see the current letter from Veolia as the output of scenario 3.
This matter has taken too long to be satisfactorily resolved and such suggests this is a procedural action and has no basis in law. In my opinion a nil response is justified. Only if real, lawyer documented, legal claim is made on the equipment are you needing to consider opening communications again.
As for emails followed by a recorded delivery letter.... that is just normal practice as an email is not guaranteed to be read by the intended recipient and read receipts are not proof of who opened the email.
If someone hopes to gain financial advantage out of this situation, remember Veolia is not known for being a generous company and, unlike Keysight, likely cares little about your view of them as a company. Expect them to play hard ball and offer you only what you paid for the item including postage, or at best, an independent valuation of the equipment in the current market. I suspect there will be no offers of replacement equipment as the discussions appear to have moved away from Keysight involvement.
Fraser