Are you actually finding the source of the punctures in each case? Is there a culprit or are there just holes appearing in the tubes?

In any case,m get new rim tape. It's likely that the bike came with a cheap rubber strip that covers the spokes and keeps them from puncturing the tube. These are crap. Replace them with a good rim tape.

I had a rubber rim strip go bad once and flatted 5 times in one day.

Or, as others have suggested, keep the tire pressure up, especially if you're seeing cases of TWO holes in in the tube which is almost certainly a "snake bite" caused by hitting something with low tire pressure.