Evri complaint: Next day delivery received 15 days later

I posted a parcel for a deadlined PIP claim on 14th Oct 25 at Walkden Post Office. The assistant told me many people use Evri next day delivery to be sure it got there on time so I paid for that service.
I assumed my claim was received before the deadline of 28th October, but it was not and the PIP people originally closed my claim because of it. I used the trackiing service and found a ‘proof of delivery’ photograph which just showed a hand holding my parcel in a car footwell !
PIP contacted me to say it was received on 29th October so they reinstated my claim, very fortunately. However, I want a refund of the postage for next day delivery because it took 15 days to be delivered.
I also want an apology for Evri’s absolutely appalling customer service. I have had a dreadful experience with a 15 email chain conversation with several different people, none of whom have understood my complaint or read the email chain. One person said since I posted it after 12 noon it couldn;t be delivered the next day, without addressing the 15 day delay or the ‘proof of delivery’ photo. Another answered me with a completely different reference number about a parcel that had nothing to do with me. most were just worded to fob me off. I am not clear on the legal position as to whether the Post Office or Evri are responsible for giving me a refund, but in any case I do expect an explanation and an apology from Evri for their complete incompetence in dealing with my problem. I have proof of posting and proof of receipt but am not sure how to send this.
If you need it could someone advise how I do that please?