The bit that you are missing is that this sort of thing is between Twilio and Twilio's carrier partners (sometimes mediated by third-party aggregators), and has nothing to do with you or your particular use case. Carriers have very low tolerance for third parties like Twilio sending spam to their customers. If carriers get pissed off at Twilio, they'll stop delivering messages coming from Twilio (or will impose other restrictions, like low rate limits, or perhaps charge more, etc.). Good carrier relationships keep Twilio running; bad carrier relationships cause all sorts of problems for Twilio and Twilio's customers.
The carriers do not know or care that the spam/fraud message you tried to send to your employee was just you forwarding along a message that some other random person sent to the Twilio number. All they would care about is that a spam/fraud message came from Twilio's platform.
Having said that, I too am disappointed in the policy of auto-suspension, and in how long it took for you to get the problem resolved, and that phone support is expensive to come by.. I think the right approach is to catch these things at send time and just refuse to send them. Sure, if some very high percentage of traffic is all spam, maybe an auto-suspension might be warranted, but I assume (hope) that's not the case for your account.
(Disclosure: I work at Twilio, though not on the messaging platform. My words & opinion here are my own, and don't reflect Twilio's stance on anything. Throwaway for obvious reasons; Twilio doesn't allow the rank-and-file to speak publicly about this sort of thing.)