Dear Unhappy. I am terribly sorry for the customer service issues you have experienced. During the coldest times we can experience high volumes in our call centers. It also sounds like we need some additional training in our personnel. As for your chimney situation, it would be best to install a 6 inch liner inside your 8x8 terracotta chimney. This is listed in the Owner's manual. The reason for this is the stove is designed for use with a 6 inch flue. A 6 inch Round flue has a volume of 339 Cubic inches per foot. Your chimney has a volume of 768 cubic inches per foot, Almost twice the air volume. This is all added air space in the chimney that the exhaust must heat so that it can rise and create the draft for your stove to bring fresh air to burn. Because of this extra volume, the air in your chimney is too cool and because cold air falls, it adds back pressure on the stove so it cannot take in as much air thus not burning hot enough to warm you. Also, our old Fisher Baby Bear was not an EPA certified stove. The Extra burn systems that are installed in today's stoves (mandated by the EPA) make them much more sensitive to the chimney size and air volumes than your Fisher.
If we can help further, we will be more than happy to do so.