Business ProfileforFatigue and Sleep Remedies

In 2020, I had a sleep study performed at Fatigue and Sleep Remedies, for which a portion was covered under insurance. I assumed I would receive a bill in the mail for any charges that weren't covered under insurance, but I never did. In March of this year, 2023, I received a notice from a debt collector that I owed $676.27 for services rendered at Fatigue and Sleep Remedies. I called the office of Fatigue and Sleep Remedies to inquire why I was never sent any correspondence to pay this debt before they sent me to collections as this was a total surprise - I had never received anything from them directly. They claimed they sent me several notices via USPS and I confirmed that my address was correct. I asked for proof that they sent me something and they could not provide it. I sent a certified letter to the collection agency informing them that I would pay the debt in full if they would agree that it would not be reported on my credit report and asked for a full deletion. The collection agency agreed to my terms, and I sent them a certified letter containing a cashier's check in the amount of $676.27 that was delivered and signed for on May 10, 2023. On October 30, 2023, I received a statement from Fatigue and Sleep Remedies in the amount of $676.27 stating that I was past due 90+ days. They are now trying to collect on this debt that they already sold to a collection agency that has since been paid in full. I have tried contacting Fatigue and Sleep Remedies several times (phone, voicemail, and email) to clear this up and have been unsuccessful in getting ahold of them. I fear that their billing department will send me to collections again due to being disorganized. I'm not sure if this is a BBB issue or if I need to contact the Consumer Financial Protection Bureau and/or an attorney instead. With the BBB's help of getting this issue escalated to the business, I hope I can "clear my name" and they will stop trying to collect on a debt that has already been paid.