I have been getting multiple calls from these peop...

I have been getting multiple calls from these people from a private number all hours of the day. They never left a voicemail. Calls received on 9pm on a Sunday included. I got an SMS yesterday so I called and gave the reference number. They said I owed $17 to TransUrban, which is the new name for Roam Express I believe. She asked me to pay immediately. I requested they email me an invoice first. She said they would do that but first I had to commit to a payment date. Again, I said no, I wanted to see the invoice first to cross check my records. She took my email address and said the invoice would be sent immediately. I am still waiting for the invoice 24 hours later.