These are methods used by skip tracers attempting to collect information and provide it to bill collectors looking for you. Most probably in preperation for a much more agressive collection methods. They will continue to call until the are able to confirm or obtain additional personal information in connection with this your number. Robo calls to cell phones should be reported to the FCC.
Try and stop them ,yes, answer them or call them back and let them know that indeed have the right number, no.

Hang up calls, called the number back and like the others said it was a prescription card service or some b.s...What is the point of putting your number on the "do not call registry" if this crap goes on anyways.  Oh, and the idiot called early in the a.m. and woke me up too.  Scumbags!

Called and hung up early on Sunday morning. I didn't bother calling back.

I got a call from 281-893-0539 at 6pm cst today. My caller ID showed it to be someone I don't know who's name being Steve Whatley in Texas. I did an Internet search and have found the source for those interested.
It's unusual that I ever get unknown calls. I think what must have happened is I recently paid for a background check on myself to see what's online about me for others to find. I used a service called intelius. Upon paying them I was asked my phone number. Intelius must have sold my contact information.
The number 281-893-0539 belongs to http://www.usrxcard.com/COH the contact info on that page leads to a
independent contract that gets paid for each person he signs up for the prescription card service.
Steve Whatley inc. of 5518 Avanak, Spring TX 77389 phone listed as 877-835-7728

maybe someone can email him a virus