Comcast is forwarding calls to the wrong number

We have two offices. If someone dials Phone number A, they get Office A, and if they dial Phone number B, they get office B. At least, that is how it is supposed to work. In fact, that is how it usually works. The exception is if the person dialilng in is using a Comcast landline. If that is the case, when they dial Phone Number A, the call is forwarded to Phone Number B, and the caller reaches Office B. It's a bizarre issue and has our phone provider stumped, since we're not really sure who can fix this. We are not currently Comcast customers, but we used to be, and we ported both Phone Number A and Phone Number B from Comcast Digital Voice to our current provider. There was probably some point in the past where we asked Comcast to forward Phone Number A to Phone Number B. Could this be related to the issue? Maybe Comcast is seeing "Phone Number A" as "out-of-service" since it has been ported to a different carrier, so they forward A calls to B?

We have been carefully tracking this issue for a few weeks now and we are certain this has something to do with how Comcast routes its calls. I have been keeping track of inbound phone numbers and verifying with the callers that they did indeed dial Phone Number A. If the caller's carrier is not Comcast, if it's any other carrier besides Comcast, the call goes to Office A. If the caller's carrier Is Comcast, the call is forwarded to Phone Number B.

Another clarification, calls made from Comcast landlines are being forwarded from Phone Number A to Phone Number B, and not directly to Office B. That is, in the call routing informaton, we can see that the call is being forwarded to Phone Number B before it goes to Office B. So the call is not being sent directly from Phone Number A to Office B.

One more clarification, we are not using Comcast for our phones. The issue is that people who are calling us from Comcast landlines are getting forwarded to the wrong number. 

Any idea who I can contact to get this fixed?