The prove up can be delayed - ask the other attorney to get a date for later in the week. If you have to offer to pay for the extra time for that attorney just so that everyone stays happy. Prove ups take about 30 minutes tops, so the judge can be prepared.
I would send a fax of a letter to your ex's attorney so that you can demonstrate what is going on.
They can say anything they want on the abandoment issue, but unless they file a motion, the judge is there for prove up and will not listen to anything else.