I would keep it simple with DL. All the minor details will only cloud the big issue.
Submit a complaint something like:
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. I was booked on XXX (with the TATL leg n PS) and after check-in was notified on a cancellation in the ITN.
. I was rerouted and eventually flew YYY (with the TATL leg in Y) and arrived a day late
I believe I am owed EU 261 compensation along with downgrade compensation
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DL will pay well when they clearly failed. See what they offer and post bask here.
[If it is nit $1000K+ cash or some equivalent deal I would push back]