Ceiling – Is it safe to drill into the metal spacer between drywall and joist

I have to ask, who gave you permission to drill into the wall? If you say your spouse, then maybe you need to take some home improvement classes at the adult education night school at your local high school! Just joking.....

But seriously, if you have run into the concrete blocks, you need to use masonry bits with a hammer drill to bore the holes, and than use masonry anchors or specialty concrete screws (tapcons) to secure the brackets to the block. The masonry screws are easiest and the package will tell you what size masonry bit to use. You can use a regular drill, but it will require a lot of pressure and letting off every 15 seconds or so to clear the dust from the hole. Don't be surprised if the screw strips on the way in, very common, it may take a couple of trys. Be sure to drill the hole deep enough. you will get the feel of it. It is not at all like drilling into wood.

I have to mention, if you have drywall over block, then there is strapping somewhere ramsetted into the block. If you can find the strapping, you can use the standard wood techniques. Look for dimples or evidence of drywall screws, that will give you a hint where to find wood. Good luck.

My guess is that it's either a sandwich beam (wood sandwiching a steel plate) or simply an i-Beam. When you drill, are you drilling through wood or just sheetrock?

If it's an actual i-Beam, you could hang it with some sort of clamping device.

I wouldn't trust dry-wall anchors for hanging a punching bag. Dry wall anchors can hold quite a bit, but not the active load of a swinging punching bag.