By "offering" do you mean that B6 has denied your request for a refund? If so, proceed directly to initiate a chargeback for the ticket price. If you have not requested and been denied a refund, do so immediately. You might try calling in the first instance, but unless you have a commitment for a refund, follow up in writing.
As with most carriers, B6 will go to great lengths to convince you to accept travel credit. Just be clear what you want and base it on the fact that it is B6 which cancelled.