Debt transfer without reasoning

I've been paying up my account only to miss one payment, now I'm called by debt people telling me that my account has been sent to them. TFG nor Sportscens called me to let me know that they are transferring my account to the debt people with a reason. I am currently paying the debt people money that I don't know about, even worse no one from TFG or Sportscens is replying back to my emails to give me a reason. My credit score is getting affected all because of them.