Business ProfileforNorthwest Bank

My mortgage payments are paid directly to Northwest on a scheduled monthly basis from my credit union. The payments are scheduled to be mailed 6-8 business days prior to the due date and 16-18 days prior to the date of incurring a late fee). I have have been paying my mortgage payments through this service since the inception of my mortgage in August of 2020. My payments have been always received on time every single month since August of 2020 (and I always pay more than the minimum). In March of this year, I received notice from Northwest that my payment was not received. I checked with my bank and the payment was sent out as scheduled. Northwest charged a late fee for this. My bank sent me a letter stating that the payment was made, with the check number, amount and the date it was mailed. The payment then finally showed up 3 weeks later. Thinking this would be a one-off situation, I didn't pursue getting a refund of the late fee, as I thought maybe it was a postal error. Then, the same thing happened again in May. My payment was again "lost" in the mail and I was charged another late fee. I obtained another letter from my bank with the date the payment was mailed, check number and amount. I called Northwest asking that the fees be waived, as I clearly (as evidenced by the letters) was making the payments each month prior to the due date. They refused stating it was not a bank error, so they were not going to remove the fees. When I talked to the first customer service representative, she did state that she had other customers calling saying that payments were not received. This sounds like it is a Northwest bank error to me. Are they intentionally "not receiving payments" as a way to charge non-refundable late fees? I pay all of my bills through the same bill pay service and not a single other one has been late or not received, so it certainly sounds like an issue with Northwest.