Hi Sukanya,
You could try using the getContextByIndex method, I think this should be able to refer you back to the correct data in your model, even after your table is sorted, filtered or column shuffled...something like this:
selectedContext = oTable.getContextByIndex(oTable.getSelectedIndex());
myValue = oModel.getProperty("myval",selectedContext);
console.log(myValue);
Regards,
Ian