"Although I could not get a straight answer it appears to be related to switching off your service for "excessive" usage."
Unless the data limits are obscenely low (i.e. <20MB/day), this is not the problem. I got the Access Forbidden message on my iPhone 4S every day for a couple of weeks, the first time each day that I moved from WiFi to cellular data. Rebooting fixes the problem, but it's still incredibly frustrating, and Straight Talk claimed to make some adjustments to my account that seemed to fix the problem for a few days, but the problem is back, and I haven't used any cellular data in the past few days except email and some light web browsing.
It's ridiculous that Straight Talk won't address the problem in the forum so that new users can know what to do to solve this problem, instead directing each and every person to private message.
I feel exactly the same way as you, while I don't want to pay a monthly phone subsidy, first and foremost I require phone service to be reliable, and Straight Talk is just not.
Straight Talk, please come clean about what this problem is and post an update in this forum instead of individually directing everyone to Private Message. So far there are no reports here confirming that you've actually fixed the problem for anyone.