Who is this... calls 6 times at 7:30pm no less.. no message... I refuse to answer.. caller id only gives number

Called my home phone.  Did not leave a message.  Call display showed DSMACS.  Called number back, but it just rang and rang.  Cannot find any info online about who DSMACS might be.

Hey I used to work for them,They are trying to sell you magazine subscriptions.

Called @ 7:13pm, I said hello twice, and then a recordinng said "Good-bye" and it hung up.  Tried to call it back, it gave me an odd sounding busy signal.

caller id says Manitoba