Well it's not impossible, in fact it actually happened to me not once but twice. I had a line that had intermittant static and hum. Probably a fault to ground and also from tip to ring somewhere between here and the CO. Line couldn't be used and trouble was reported but it took the TELCO about a week to fix it.
Because of this condition the line would sometimes go off hook at random. Not random enough apparently because at 2:30AM my doorbell rings. Cops are walking around the house and want to know who called 911. I tell them nobody that it has to be a mistake. They kind of believe me and go away. I was half asleep and didn't bother to ask them where the call came from.
A couple of nights later almost the exact scenario. Middle of the night, cops at the door, 911 call. This time I question them about what number the call came from. It was the line that was out of service for a week! That thing dialed 9-1-1 all by itself TWICE. I took the cops in, handed then a phone and said see if you can make a call on this line. Case closed.
I'm not saying that this is what happened in your case but consider that some TELCO's may not disconnect a line, only restrict service when you request that the service be disconnected. Possible also that in such instances only 911 calls can be made much like an old cell phone that has been disconnected.
-Hal
