I am not sure you do understand the best way forward for you. You should post a new thread asking for assistance on that. Your best path is probably to use a private CA. That would give you complete control of the certs. But, for a public CA you should be trusting roots and NOT PINNING intermediates. Even roots will change over time. These are the first things Let's Encrypt warns about in the Integration Guide: Integration Guide - Let's Encrypt
With that said, staff monitor this forum and they would need to divert efforts for your case.
There was a similar situation last summer where @aarongable, a member of LE staff, said this: Is there any way to resume R11 in Let's Encrypt - #5 by aarongable
A review of another thread by Aaron from 2020 is also instructive: IOT Devices with X3 certificate embedded - #13 by aarongable
The R13 intermediate you pinned to only started use last August. I applaud your ability to obtain a large installed base in such a short period of time. People using such new products are often understanding of the "growing pains". Yes, it can be painful but in the long run can build trust with your customers. I speak from personal experience of running a tech company.