Nationstar Mortgage Mortgage Complaint

Nationstar Mortgage Mortgage department,

Home equity loan or line of credit Loan servicing, payments, escrow account Illinois

My service provider - sold my mortgage loan to Nationstar in - of 2014. I have been having issues with the way they allocate my monthly payments to my account. The applied portions of the payment to principle and interest is not being done as it was with the former provider. I have also gotten statements that show no amount due for the months of -, -, -, - and -. - was the only month there was an amount due shown. When I called the customer service about it, I was told they would check it out and have it corrected. I sent an e mail to their research department and got a response saying I did not make a payment in - and the account was overdue. How can an account be overdue if the statement shows no amount due. I have spent several hours on the phone with their customer service and loan specialist with no satisfactory resolve to the issue. I need to know what to do to get them to correct the way they are handling my account. Please advise me on this matter and let me know what kind of documents are needed to pursue action and resole the issue. This was originally a home equity line of credit account which the provider is no longer honoring the line of credit portion. I did not authorize any changes to the original loan terms, but the new provider is not following the same procedures as the original provider when it comes to billing and accounting.