Drain Field needs to be replaced?

My husband and I bought our home about 1 year ago, it is a 3 br 2 bath and is about 1200sq ft. We found out that the couple we bought it from had it listed and permitted as a 2/2 with an office as the septic system was only set of for a 2 bedroom dwelling. The couple told us the septic was pumped about 1 month before closing, well about 5 months ago we noticed a horrible smell anytime while being outside, so we looked and looked and could not figure out the issue. Then our dog was outside and we noticed her digging, we got her away from it, and returned back out to try and figure it out. We called a septic company right away, he came out and stated we should try pumping before anything further. He then came back out and opened the box, and it was the nastiest, smelliest thing I had ever seen. He told us "That this is the worst I think I have ever seen, It does not look like it had been pumped in over 10 years." I mean there were plastic bags, wash clothes, plastic forks, you name it and it was in the tank! I was so embarred, I could not believe what all three of us were seeing. Well, we noticed that it seemed to work...or that's what we thought. The couple that we bought our home from, also owned the home behind ours as well. They sold it about 2 months ago. We seen them outside and having the same thing done, they were going thru the same things as we were. They had been told the very same thing as us. They just had there entire system (field replaced) We called the county inspectors out to try and see if we could finally figure out the problem. The inspector did something with the lines and it worked...Again so we thought. The water stopped puddling up in about 3 weeks and we thought we were in the clear. Then we washed about 3 loads of laundry and the water was in the yard again, and when it rains good the water is there. I called our homeowners and our agent said we are covered, that we needed to file a claim? I have never had to file any type of insurance claim and I have no idea how it works? I was wanting to gather some Information on what replacing the drain field may cost. Any help is very much appreciated and thanks in advance. The coverage that we do carry is $6,000.00 with a $150.00 deductible, I am just unsure if that will be enough to fix our problem? Again thanks so very much!