Transworld Systems Inc. Debt Collection Complaint

Transworld Systems Inc. Debt collection department,

Medical Communication tactics Threatened to take legal action Arizona

I have received no contact with anyone regarding a bill that I owe. I just received a letter in the mail from Transworld Systems Inc, stating that I owe them money. They advised if I do not contact them within 30 days after receiving this notice, they will assume the debt is valid. I have tried to contact them by phone and have been unsuccessful. The voice mail that I was connected to stated that it is full and I ca n't leave a message. How can a company just give you 30 day to prove the debt is n't your when you do n't even know what it 's for in the - place? Is this company a fraud?