Payday lender did not sign my certified ACH revocation letter

I followed procedures of revoking ACH for several payday lenders. Some complied. One did not, and in fact debited 2/3 of the original loan (something in the fine print I did not read perhaps? - learning lessons the hard way), leaving me overdrawn. Also bank issue - they didn't block it even though I provided copies of the certified letters I sent along with the receipts. I will file a dispute with bank, which to my understanding is their policy, even though I explained the laws (REG E) that I read about. More stalling, I imagine. Anyway, I tracked the letter I sent to the lender, and USPS said, "no one was authorized to sign for the package." Meanwhile, I sent the letter directly to the Collections department in plenty of time and not during holidays! Are they scamming me? Do I send another letter? What if I call and verify address? How do I know the same won't happen again? I am learning as I go...I am sure this will be a painful process, but it's a life lesson. Thank you for any advice you can give