All of our outgoing e-mails and faxes are now blocked

(apparently by IP proofpoint, which apparently RC contracts to prevent outgoing spam). We had to move a mile away from our previous place of business, but it was in a different town, so we had to switch from DSL to fiber. It meant going from our prior IP address to a temporary one with a modem, to a final IP address when the fiber was connected, but as soon as we had the final IP address we lost all functionality for outgoing e-mails, and e-mail faxing, which is huge. It has been over a week, with multiple futile attempts to reach RC via the bot, two in person calls totally about an hour with no resolution, and follow up e-mails telling me that RC was closing the case; we have sent multiple requests to proofpoint to unblock us, spoken with the people with our ISP and I am at my wit's end. Anyone with any ideas (other than ditching RC, which is looking increasingly likely)