How do I contact this VERY unprofessional company????

I discovered with utter shock how unprofessional this company is. They sent me e-mails from different collection agents, and i reply to each and every one. I also try to phone all numbers on the e-mail, with no luck ( I get, this is the wrong department, and they put down the phone in my ear, numerous times!! I also sent a whatsapp (note that they spelled this incorrectly on their correspondence) to the number they supply. It does not get read, although i see the ONLINE on the number. Then they still mention "despite any efforts to make contact, we have been unable to speak to you" How on earth must i contact them?????