Want a quick solution?  Grab your smartphone, your regular phone, and your work's fax machine phone number.
Get your smartphone ready to record (open the "voice recorder" app).  Then call your work's fax machine line, and record the tones when the fax machine picks up.  Let it record until the fax line hangs up (about 1 minute).  You're ready to have fun, now!!!!
The next time a telemarketer calls, open up the voice app and PLAY the fax machine recording when you answer the phone.  It usually takes 5-15 seconds for the telemarketer to hang up.

BONUS!!!!!   Your phone # will be marked as "business - fax" on their list (basically a useless number, since you can't scam a fax machine).  So you won't get repeat calls, and when the people who have you number sell their lists, your phone # won't appear on it!!!  Basically, your ## become useless to THEM!!!  BWA ha ha ha ha!!!!!!!