While I assume you've probably done this, you can try going up the chain, telling the higher-level managers just what a shitty experience you've had, and that you're considering looking elsewhere to fill (some of) your needs as a result. You don't have to say you're considering moving everything, just that you're going to start experimenting with other providers where appropriate, and start breaking the MS stranglehold on your business.

Make someone important start genuinely worrying about your account. Get them to assign a permanent engineering contact point, since it's clear your account manager isn't doing it for you. If you're not a manager-level staffer, get managerial support in doing this, so you have their backing and they don't undermine you later (even accidentally). And while you don't have a blog of your own, if you get stonewalled again, you could reach out to a tech blog with a decent amount of penetration and have an interview with them - either about the shitty experience, or the thought of moving vendors and implying that MS is no longer the only game in town for your -foo-. It doesn't have to be perfectly true, it just has to generate visible bad press - it's an underhanded tactic, but if you're consistently being treated poorly, I think it's an option to consider.

Or, even better, move off MS where possible, and spend that money on staff to massage the changeover :)