Product: Mortgage

In late XXXX my mortgage co did a loan modification which left us with a difference ( their documents support ) however they applied funds was their discretion. Fast forward to XX/XX/XXXX they sold our mortgage and the first payment due from transfer letter, {$2500.00} was due to the new mortgage co on XX/XX/XXXX, XXXX payment to previous lender was paid and I called in the XXXX payment to new mortgage lender. We paid this payment and about a week later received our first statement from them which said we were behind {$10000.00}., we were shocked! So I called in to inquire ( again ) and they said the loan was too new and it only shows the current balance due as {$2500.00} and to give it a few days to update that all funds from previous mortgage co be applied. About week or so goes by and my door bell rings and there is a lady handing me a letter from this mortgage co. Im astounded that they sent someone to my house instead of just call or send a letter in response I did not like that at all. It simply stated they had been trying to reach me yet NOONE had reached out via phone, voicemail, email or standard mail. 
I then called to inquire why send someone to my home and not call me and the agent stated they see where I was confused and they agreed looks like there is an error that he couldnt figure out why it says Im behind. He stated he will put in a form to track payments and fees that had been paid/applied and I should receive a letter. I receive a letter that they are reviewing documents however the next month comes I receive that monthly statement ( date XX/XX/XXXX ) which says I owe the normal amount and does not have any past due. At this point I think, " ok they have figured everything out '' ... NOPE... I recieve a letter ( dated XX/XX/XXXX ) now its past due again {$5900.00} and that will be reported to credit bureues ( as if I havent reached out ). 
Then another letter on XX/XX/XXXX stating im two month behind and my loan is in default. Demanding payment and now {$880.00} in fees.. Again no response to my call with how Im past due when these months were paid and no mention as to this could be from transfer error or lets help look into this. Again I just started with this company in XX/XX/XXXX and have paid these months with them. I call again the agent says she will be able to help and putting in a " form '' and that she will call back with answer, no call... 

I then receive my statement that has me once again now past due even though last statement sent wasnt.. I call because I cant pay online due to them wanting payment in full ( even funds that are in suspense that are not applied ) I pay over the phone and inquire again for help with where I am past due once again providing proof last mortgage co has statement date and amount due and amount past due ( {$0.00} ) on its statement why are you saying Im past due? Agent just states she will inquire for me she cant help. 

At this point I send a certified letter on XX/XX/XXXX " notice of error '' requesting them respond in writing. -- -- -Nothing. 
Then this Sunday XX/XX/XXXX around XXXX my door bell rings another hand delivered letter from this mortgage co stating they are trying to reach me and to call them..Im so upset at this point because I just spoke on the phone with them.. I can not get help with this company please help me understand why they are not being transparent about this transfer?