Look at it from the client’s point of view. If your company is not willing to listen to a customer that provides 75% of your company’s sales revenues, and being that the GM has had 1 year to get things in line and has done nothing to appease the customer, would you want to retain a supplier with that track record if you were the client. Does make one wonder if the people the GM is accountable to are aware of what has gone on.
I don’t believe that there is anything that can be done at this time to retain the client. Time is up.
Good work. The key here is you did not want to be trying to go solo on this one. Worst case could have been a lawsuit in that case because there’s no way you could have controlled the situation - at minimum the client would have mentioned they talked to you. Spreading out this info and offloading the decision was by far the best move here.