Why does my water stink?

I live in the country and I have a well. my water began to stink and i lost a lot of hot water so I checked out my water heater and determined that the lower element was bad and since the heater was at least ten years old I opted to get a new one. I bought a Whirlpool Gold water heater with dual anode rods, larger elements, and energy star. the heater was the most expensive 50 gallon that I saw there at 500 it has a 12 year warranty and I installed it myself. I figured that that would solve the problem but after two or three days my water began have a sulfuric smell again. I am wondering if it is my water softener it is a rented one from culligan and has been here since we got the house 9 years ago. we have had various issues with it and every time they come out spend 10 minutes charge 50 and say that it is fine. it is not consistent in putting out soft water, and uses 200-250 pounds of salt in a week to week and a half. I also have to clean a disgusting looking black sludge off of the side of the brine tank 2 or more times a year. what should I do?