Well, the graft should be exposed, anyway. You want to just barely cover the "root flair", where the topmost roots emerge from the trunk. Being buried too deep over the past year may have done the damage--what is the state of the bark between the graft and the root flair?

Thanks for the reply, Well, yes, probably the graft should be exposed, but not this much exposed.I recall following the instruction card and it saying the graft should not be covered, but not in as many words. The apple tree that I planted next to it all on the same day is bearing fruit, no different planting regime, no different soil mixture and no different approach, however apart from following the instruction card, regarding the planting, really I know nothing about fruit trees as I have never planted a fruit tree in my life before these.

Here's a good illustration of how a tree--of any kind--should be planted
http://landscapevermont.com/spring-clean-up-and-tree-ring-mulching/
When trees are planted too deep, the buried bark smothers and dies, or is killed by various collar rot fungi. When that happens, the sugar produced by the leaves can't get down to the roots, and the roots eventually die of starvation, sometimes several years later. Apple trees are more resistant than pears, but I would still inspect the buried bark of it, too.
Another possibility is that it contracted fire blight, a bacterial disease spread mainly by dirty pruning shears, and occasionally by honeybees. Don't curse the bees, though--without bees, there are no pears! Fire blight rarely outright kills the trees, though.