Can my service provider tell me who an unknown call is?

Generally no. If it's harassment or something I believe you have to go through the channels of the law... otherwise I don't think so.

Can my service provider tell me who an unknown call is?
I swear to the heavens above, I will dog your steps every last day of your life Dr. Kimble

Actually its pretty serious. I'll file an official report tomorrow and let the authorities get it. Sucks because that halts me from doing what i want to do about it. But fair enough.

If it's to a phone # you actually pay for by the minute (e.g. toll-free or wireless minutes), you can usually wrangle your carrier to get the ANI for a particular call without a ton of horseshit. The worst case is arguing that you never received such a call and ask them to prove it, waive the charges, or take them to small claims. But, you start out much more civilly than that, politely escalating to customer service managers until you get joy. If it's a serious harassment issue, see if harassment is a fast track to getting what you want, otherwise go to law enforcement. If customer support doesn't provide joy, go to the MPSC.

Your carrier knows who to bill for the call, the ANI, in a way that may or may not give them enough info to know specifically who originated the call. The info should be enough for the originating carrier to figurer it out, though. If you get the ANI from your carrier rand it's not obvious, you take it up with the carrier who made the call. Since you probably aren't paying that carrier money, they may not have much of an incentive to give you customer info.