1. Simple solution- get a piece of corrugated plastic of the type that estate agents boards are made of size about 20" x 20". Buy a pack of blue carpet tacks (cost about £1.50) Press the carpet tacks through the corrugated plastic in one direction spaced about 2" apart. If you want some plastic, PM me your address and I willl drop some off if you are not too far away.
Place the spikey plastic mat on the floor fixed with a few dabs of blu-tac under where your bag is hanging. That should sort him but whatever approach you take to solving this problem be prepared for foxy to take his revenge on you by leaving a "deposit" on your doorstep.
2. Make up a chilli and mustard sandwich and put it in a paper bag and leave that there overnight so that foxy gets to it before the delivery.
3. More expensive - buy a mesh box, like a cat/dog carrier and place milk etc inside but kake sure itt is firmly anchored as foxy will work on it.