Security Finance

got a small loan for $388.18 with Security Finance back in December 2012 and since then have mailed them my monthly payments of $75 plus an additional $25 each month which was due on the 29th.Each month after mailing my payment I saw that the check was cashed either the next day or 2 days later and was applied to my account. On Thursday May 23rd I called the Lebanon office to find out my payoff amount. I made a check out for the amount I was told and mailed it to them that same day.
I expected that this last and final payment would clear my bank and also be applied to my account within 2 days yet on May 29th when I checked my bank account I saw that it had not cleared my bank yet so I called Security Finance to ask why. I was told they had not received my payment. The lady sounded nervous on the phone and when I assured her they had to have received it I mailed it 6 days ago she told me that maybe the post office misplaced it, she remembered me calling Thursday and would make a note of my call but that I now owed additional interest and to call back tomorrow by 3 they might get it by then.I am very upset because I do not believe for one second that my payment was lost in the mail. I had this EXACT same thing happen with them several years ago with a different loan I had with them and again it was only my last and final payment that coincidently got lost in the mail.For this to happen to only my final payment not one, but 2 times is more than a coincidence. I honestly feel they received my payment on Friday the day after I mailed it and they are not applying it to my account so they won't miss out on month end bonuses or something. I understand this is a serious accusation but I am not the only one who has experienced a lost final payment with them.I called the Post office and spoke to the delivery superviser who told me they had received numerous complaints from others who had mailed final payments to Security Finance and other finance companies and also reported them as missing. It only seems to be the final payments that ever get lost yet the post office has no way of knowing they are delivering a final payment so there is something very wrong here!
I have never had any mail lost with the post office in my life except for 2 final payments I mailed to Security Finance and one to World Finance.I know in my heart that my payments were delivered on time and just not applied because I did not use delivery confirmation and this is too big of a coincidence. This is a very shady way to treat customers and according to the USPS delivery superviser it is a problem others have as well and for Security Finance to get away with this is very wrong. I feel it needs to be investigated and I feel people need to know how this office is doing business.