A bunch of useless turds, chasing & threatening or...

A bunch of useless turds, chasing & threatening ordinary people who are being ripped off by major banks, Telcos & carriers, utility providers
Always ask them to provide proof of the debt
Ask them to provide signed copies of terms & conditions from ISP's or carriers, or verified voice recordings that clearly show you agreed to pay the EXORBITANT charges
Make it difficult for them