SE is not level3's customer...nor Cogent's or Tata's, etc. But...your ISP is.

Need to get with their Tier3 support and provide them some specifics about your connection, and push them for escalation. You are paying them for the service. Demand they properly support you and remember...they answer to a regulatory authority (at least in the US--contact details are supposed to be provided with your bill). Ideally, you want to send both a good and bad trace to the IP that your client actually is using while in game (netstat or resmon will provide it...Canadian servers start with 199). At the very least they need that IP address.