Re: I work in customer service...
Hmm. Hate to just be a nay sayer, but I'm not sure number 1 and 3 there are the best ideas. The average creep likely isn't going to care whether you're single or not. It just unrails the conversation towards the exact personal matters that you don't want to talk to them about, and keeps them on the phone. If you feel the need to say anything to make it clear you're not interested/available, just keep it very short and plain, and try not to give them anything they can latch onto.
The third one I probably don't need to elaborate on. Same reasons as the first, in addition to how I assume the calls are recorded, and can probably be overheard by half a dozen co-workers. I also really doubt trying to spook em with stuff like that would work in any reliability. >_>
The second idea is probably the by the books policy, though I have no idea how well that works myself. I assume you've tried it some. Polite but to the point and all that.
Have you tried asking your supervisor or co-workers for tips about these types of calls? I'd bet most of them have had to go through the same and at some point have dreaded or groaned at such calls themselves.
[edit]
Beaten by Obs. But everything he said too. In general, it's probably a bit like trolls. "Don't feed the creep". There will be a variety ranging from slightly distractable people, to outright creeps only on the phone because they're bored. Both of them are fed by personal reactions and emotional responses. I'm not exactly (read: remotely) the kind of person qualified to say, "be assertive", but that seems like the order of the day.
Additionally: Don't be creeps to phone ladies guiz. It's bad. Also silly.