Turns out it was a routing problem - but I don't know whose end it was on. And it's fixed. Others with 343 area codes should be able to dial 811 in Ontario now without problems. If not, they should report it. Thanks.
Public Mobile is working on it. Apparently, the situation is problematic with some 343 area codes. Telus (PM parent company) followed up with me and they are trying to figure out what the problem is. Thanks though.
