Complaint

I've settled my account and I was promised a settlement letter within 24 hours of paying, this is after getting calls daily harassing me to pay. I've been over 2 weeks and I haven't received a settlement letter after making calls daily requesting this letter. Instead I'm given invalid number to their customer service department where I'm unable to get through to anyone. This is very upsetting and very unprofessional, no one wants to take any accountability at all. Can something be done about this