What's wrong with my apple tree?

Three years ago we had a bumper harvest from our eating apple tree, type I do not know as it was with the house when we purchased it. After that big crop we had the tree pollarded & the following two years have been awful. The tree produces a big crop & they start to ripen but rot on the tree before they are ready.
Does anyone have any tips to what may be causing this? 
Do we need to get rid of tree as we have a cooking apple next to it, but this seem ok & don't want it to go the same.
Any information would be great fully received.
Many thanks
Kevin