[PHXFlyer]

The initial change was voluntary and I'm guessing the $1300 you paid was a combination of the change fee and the additional fare for wanting to leave a day early. When you purchase a ticket in advance and then change the departure date the ticket is re-fared as if you were buying a new ticket. If you no longer have a one or two week advance the fare will almost always increase significantly.

When the flight on the new departure date canceled you had the option of a full refund. Since you obviously still needed to travel to Halifax you opted to re-schedule to the next day which, coincidentally, was your original departure date. My advice would be to pen a concise letter to United detailing what happened and request that the difference in fare that you paid plus the change fee be refunded since you paid a premium fare to depart a day earlier and United did not deliver. If they do not respond favorably there is little you can do as it is within their contract of carriage to charge you the higher fare for a change initiated by you. Your last recourse would be small claims court and you can hope for a default judgment should United fail to appear.