Lawn topsoil /subsoil

I built a house on a sloping site approx 10 years ago. I wanted to raise one section at the base of the site near the road exit. I asked the excavator at the time to strip back the topsoil, increase the depth of the subsoil and replace the same topsoil again. When i got back the job was complete and he said he had to use additional topsoil i had on the site. No problems of course until he is paid and out the gate. Soil settles, rain comes and year after year a person cannot even walk the lawn its so wet and soggy. The surrounding lawn is bone dry except for the raised section. I decided to dig some deep trial holes in the area in question and this confirmed the worst. So now i have a later of topsoil, a layer of subsoil (10″) and then the original topsoil again below that. Firstly would this explain the wet ground and secondly have i any option except the obvious and strip back the ground again?