Product: Payday loan, title loan, personal loan, or advance loan

My husband and I did a refinance on our home to help pay off some bills. We had checks mailed to pay off both of our open loans with this company ( Upstart ). We were given payoff forms along with the mailing address, processing times etc. 
The attorney mailed the payments on XX/XX/XXXX. We were told since they went regular mail they would be applied XXXX days from receipt. Per a conversation with a representative ( XXXX ) on XX/XX/XXXX, he stated that they didn't show receipt of our checks at that time, he suggested to stop payment and resubmit the checks via overnight as they would process faster ( XXXX days ). The attorney stopped the payments with the bank and resubmitted new checks that were overnight on XX/XX/XXXX and per XXXX  XXXX were received on XX/XX/XXXX. 
In the meantime, the original checks suddenly appeared and were posted to the account. They of course bounced back per the stop payment. 
On XX/XX/XXXX I started calling as the XXXX checks should have posted by then however they still weren't and interest was accruing daily. I spoke with the following people : XXXX, XXXX ( twice ), XXXX, XXXX, XXXX, XXXX, XXXX, XXXX, XXXX and XXXX. 
They all stated that they would notify the " back office '' and start an investigation on why the checks weren't being applied and get back to us. As of XX/XX/XXXX, I called every single day and was told the same thing. The reps could not help me, could not transfer me to anyone that could help me, the " back office '' could not be contacted etc etc etc. Finally on XX/XX/XXXX, the XXXX check was applied to my account and per the website, it " errored out '' and could not be applied to my account. I called yet again and at this time had the attorney do a conference call to find out why. He checked with the issuing bank and they had plenty of money to cover the check and the bank said that the check was never processed on their side so Upstart never applied the check or did so incorrectly. 
We called XXXX more times. Once were hung up on, the XXXX put on over XXXX XXXX hours hold time until the call dropped and the XXXX time were told that they couldn't help us find out the reason for the error. 
Now it's been over 30 days, interest has accrued daily on both accounts and no one at Upstart can help. They say they are opening investigations but nothing is done and no XXXX ever contacts us back. We have had to call daily to find out what is going on and again, get nowhere. 
I did get a call back finally last night ( XXXX ) however I asked what their investigation found and she simple stated " we did not find a reason '' and again, could not help at all. 
The attorney has just stopped payment now on the XXXX check because now they are saying they did not receive the XXXX check for the XXXX account. We had to stop payment on the XXXX check as well so that he could wire the money to me and I could pay directly. Upstart would not take a wire directly, would not let them apply a payment as a third party and until the stop payments were made on XXXX checks, twice, because they can't tell us why the XXXX check errored out. 
Upstart is purposefully postponing our pay off as they can just say it's " in processing '' or they dont show receipt so they can continue to charge late fees and interest. At this time I have applied payment in full to both accounts however they are now outstanding a months interest in the amount of almost XXXX additional dollars. 
We are seeking help in getting all interest accrued from the XXXX check receipt date of XX/XX/XXXX to current.