PHH Mortgage Company review: I'd like legal documentation with original contract

My Dad has a Reverse Mortgage and has been going through Champion Mortgage. My Mom made an aggreement with this company to pay 500.00 monthly before she passed on12/28/20. We have been making monthly payments over the phone with no problems. On Feb 23, I called to make the payment and was told by a Rep that a new company PHH bought them out and they gave me a phone to contact them with further payments and was told we would be receiving documentation stating this company was taking over with original contract and PHH would also be sending us a " welcome packet" explaining their services I was told Contract would carry over, that 500.00 would be paid monthly. In March I called to make a payment and spoke with a woman Paige . She told me payments were not allowed to be taken over phone and gave me the address to mail it to along with Power of Attorney papers bc I take care of my Dads bills. That same day I mailed a check for 500.00. 2 weeks later my check was returned stating they have no contract stating this aggreement. I called and confirmed they had POA papers. I was told I would be receiving a welcome packet with original contract from Champion and a new contract that needed to be signed and sent back. I have tried numerous times to call.I have not received anything from them. Each time I call The Representives are extremely rude and not helpful.I have been hung up on and yelled at. Im trying to get this taken care of and am getting no help . I dont want my Dad to be penalized bc of their incompetence. They have the POA documentation, it was confirmed! They still insisted on talking to my 91 year old Dad for verification. They asked the mailing address and my Dad told him all his mail comes to my house. The fact that he did not know my zip code they refused to talk to us or help us. I have never dealt with such a rude company. We know nothing about this company, have no documentation from them and are getting no where. This has been going on since February. I asked to speak with a Supervisor and was refused . I am absolutely disgusted with the rudeness and their lack of Professionalism. I dont know what else to do