I too have been getting these calls for weeks every morning around 8am. They don't leave a message and I have never tried calling back. This is on my landline. But... the name on caller ID is Wm Malone not octothorpe.
I also received at least one call a day from 202-540-5120...decided to call them back today. It is an ATT affiliate and when you call they have a recorded message that you can choose option 1 and be placed on their do-not-call list. Says it will take 24-48hrs to take effect...we will see.
What I thought was odd was...the one time I finally took the call, I asked the person, "What is Octothorpe?" and she replied plainly, "I don't know." That would be funny if it wasn't so stupid.