Hyundai Motor Finance Lease end issues Nationwide

 I returned my leased vehicle back in January. After the fact, Hyundai Motor Finance took an additional payment out of my account. I called the next business day (the 3rd week of January) to get a refund and was told it would take 10 days.Two weeks later I still hadn't seen anything and called back. They said there was an error and they'd get the refund filed. In March I still hadn't seen anything and called back yet again only to get the run around again. Monday, March 31st I finally got to speak with a supervisor who stated he'd personally handle it and see that a refund check was issued and would call me back at the end of the day. I called him every day that week with no response. I called April 7th and was told by a lease end person (not the supervisor) that there was no change. Today, the 10th, I was told that they still hadn't issued the check! I can't get the supervisor back on the phone and apparently the lease end department is 'the only department that can assist me'. Lease end is not doing their job and it shouldn't take 4 months for a refund!