Record -0° temp in Arkansas and my '10 Jeep Grand Cherokee is overheating plus heater stopped working

I had a good amount of 50/50 AF but when the temp dropped to record low of -0° my heater gradually went out over several days. I added a little concentrated AF and next day it overheated. Should I replace the water pump? Do I need to flush the coolant? Is concentrated AF bad? 2010 jeep grand Cherokee.