What does one do when the lien holder isn't cooperating with the final payment arrangement of financed vehicle, and holding title?

I purchased used car from car lot, and financed through their referral. I have fulfilled all of my payments but they continue to asses late fees and surcharges to make it appear there is still a balance owed in an attempt to hold the lien and charge me. They have absolutely no contact number except one that receives messages on, and will not cooperate with my attempts to settle out the account by speaking. They continue to reflect a balance on my online portal in an attempt to justify not releasing the title, but they have not provided me with the means to achieve this goal. please advise