Either the store manager is bluffing, or Sony have actually stated that the device was abused by excessive pressure. On touch screen devices, different people have different pressure margins, but having said that, the item should be solid enough to make it 'fit for purpose'.
There is the other point, that most Sony store are franchised, and this in itself might lead to a differ of opinion. If there is a form of Trading Standards or CAB in Oviedo Spain, then perhaps consult with them, or alternatively do a web search, to see if there are any similar reports to the problems you have. Then go from there?.