KLM claim adverse weather

My first ever post so apologies for such a long rant
On 4th Sept 2019 our flight KL960 from NCL to AMS was delayed and we missed our connecting flight KL617 to Boston
When we checked in at NCL at about 10.30am ( the scheduled departure of KL690 was 13.15) we were told that already our flight was showing a 20 minute delay but no reason given. As we waited in lounge our delay grew longer and longer as all other flights continued to land and depart on time. At 15.55 before we had left NCL, we got emails from KLM saying that we had missed our connection and were being rebooked on flight the following day No reason was given for the delay. As we boarded the delayed NCL flight the gate agent already knew we were rebooked on flight the next day. No reason for the delay was given. When flight KL690 finally departed NCL the pilot gave a very short apology and said something about problems in AMS. In all of this adverse weather condition was never once mentioned.
At Schiphol we were told to go to Transfer Desk 6 where we joined a long queue of unhappy customers. Eventually we were booked on DL257 for Boston at 14.40 the following day 5th September and given hotel accommodation for the night.
The next day DL257 was further delayed so we eventually arrived at or final destination over 24 hours late.
On 26th sept on our return to the Uk I completed an online form with KLM for Flight Delay compensation, 24 hours later I received a poorly composed, cut and pasted template letter full of major inaccuracies about our onward journey and rebooked flights! And our claim was declined as "there was adverse weather condition which caused delay to the incoming flight" It was complete nonsense and clearly our claim had not been read carefully. I immediately sent a second email pointing out these glaring errors and asking for someone to read our claim form more carefully. Nothing happened after a few days so I phoned KLM and was eventually told our case had been closed and no one had bothered looking at my second email . Someone eventually looked at my response and very shortly I got another Cut and pasted letter still claiming "adverse weather condition delayed incoming flight etc and that my compensation could not be paid. he also added a suggestion that I "should contact National Enforcement Bodies to get “the exact disruption reason”!" (So is “adverse weather NOT the reason? What is known and KLM made passengers aware ahead of time, is that there was a 2 hour scheduled strike by KLM staff at Schiphol on the morning of 4th Sept
I then sent a NBA letter. Once again nothing happened and once again I telephoned. Once again I was told my case had been closed and once again no one had read or acknowledged my NBA letter. I then asked for a deadlock letter and that duly arrived.
So.…………….having read hundreds of posts and Vauban's- Guide all extremely informative and helpful should I go the aviation ADR route or jump straight to Small Claims court or NWNF firm. Or did I miss some "adverse weather condition" on the morning of Wednesday September 4th?