We were paying them around $1500/mo and had a similar issue where they blocked some (in our case) legitimate messaging traffic. We switched most of our traffic to another provider and are pleased. We had been a Twilio customer since 3 days after they launched and I owned a significant amount of their stock. I sold it all when this happened in spring of last year and I'm glad I did... stock has gone down significantly since. I don't see Twilio doing well long term, they provide an API for a network they don't own.