Route 20 is a Canadian carrier. The likely reason you had trouble was because some US toll free routing won't route from Canadian carriers properly (I know this because I have to use voip.ms to route my calls via a Canadian toll free carrier, otherwise my companies I manage can't call the Canadian government, ie the Canada Revenue Agency AKA IRS of the North). I would be inclined to block 28 as well (Iristel) for toll free if I was in the US because they are also Canadian. Iristel is actually a pretty good carrier apparently; ISP Telecom has had some weird outages over the years. I would actually have to do the reverse and block everything except those two, except voip.ms does a better job anyway as they can route 311 (municipal services) calls also in Canada.