Sharraxaadda

I get a special food delivery every night. Someone started stealing my food bag. These are delivered later at night usually between 12 & 1 o'clock . Then I started chaining it to my lock box and delivery has key to take empty and leave new one. Now someone is cutting the plastic tag and taking food out of bag. This food delivery is very expensive and I am a disabled senior citizen. Do you have any suggestions. My door is directly on the street and as I said he comes rather late to stay up and change bags