Have you set up a call-forwarding number at the campaign level but the callbacks are still going to your master call-forwarding number?
If someone is calling back from a number that is not in that campaign, the call will go to your Master Call-Forwarding Number as the system has no way to know that that number belongs to that campaign forwarding setting.
IMPORTANT TO NOTE: We do have a blocker in place that will restrict non-prospect phone numbers from being forwarded. This is included to avoid unwanted calls that may be a result of spoofing.