Is the 220V mains voltage?
If its mains voltage, you need to have some form of isolation between your circuit and it. Perhaps a sense transformer or an optoisolator.
If its not mains voltage, and its already isolated from the outside world, then you may be okay measuring it directly using just resistors however I would arrange things so that there is high impedance of some kind between then 220V and the rest of your circuitry. I.e. a series resistor that:
-could safely shunt the 220V directly to its return (power rating and resistance determined)
-will limit current into whatever is connected to it to below its maximum rating
Note that a series resistor like this may affect the performance of your differential amplifier and/or PIC A/D, so you will need to find a balance.
I would also connect limiting series resistor to your current shunt, so that in no situation could the 220V somehow directly reach your low voltage circuitry unless it is such a high impedance that it wont have a damaging effect.