Periodontist filed claim with missing information, now keeps saying they refiled the claim but the insurance says they didn’t get anything new (Maryland).

I had a dental procedure in January at an out of network provider because I like the periodontist and his office assured me that they still file a claim with insurance. I had to pay up front out of pocket and then they reimburse you once it goes through insurance.

The first time the claim was denied because they did not provide all the information to the insurance. After this I called multiple times and every time it's the same story of "We submitted the information, check your patient portal in a few days". This has happened 4 times now and every time the insurance says they didn't receive anything and at this point I am inclined to believe them because the periodontist keeps "submitting" things every time I call. So either they are lying to me and haven't submitted stuff or they are submitting it incorrectly.

Is there some complaints process I can follow for this? The only way I can get a hold of them is over the phone so I do not have a paper trail of emails. Only the initial contract I signed where it says they reimburse you after the insurance claim.

My dental insurance is through Humana.