I get how difficult it must be to answer phone calls from sales people, day in and out, incessant calls from the overly aggressive and the seemingly undead, at least when it comes to persistence. No wooden stake ever stopped one of these guys, and I'm not aware of a silver bullet that works in all cases.
In this day and age that description fits very few salespeople I know.
And yet perfectly reasonable professionals hide themselves in plain view at networking events, saving their hob-knobbing for old friends and associates. They leave no trail at trade shows. When contacted they become reclusive and surly, ("where did you get this number?") presumably to avoid prospecting calls from the likes of yours truly. That hurts a little because I'm not just robo-dialling from a purchased list. I've done my homework, I suspect you need or would benefit from knowing about my product. You represent what seems like a cool organisation, the kind with which it would be an honour to do business.
You're the customer, you hold the cards and I'm sorry for whatever has happened in your past that makes you wary of all salespeople, new products, change, new approaches and better results. I am in no way suggesting that your current provider isn't the very best you can do; I am strongly suggesting you don't know that for sure.
I further respectfully suggest that the problem may not entirely lie with unprofessional sales people, though I acknowledge such individuals do exist, but in an adversarial view that is preventing us both from reaching our true potential. Someone's customers and members, as well as their organisation's bottom line, may be suffering as a result.
Plus, rumour has it you're a decent human being and a respected professional in your field. No reason you should care, but I'm going to be worse off for not having met you.