When the audit office investigated (they found that) it's the same people that buy a lot of these coupons. There was an occasion where 1 million Yen was spent in one shopping trip. People from the same company bought a total of 18 million Yen's worth of coupons, and there was a time they were even used to buy a boat.
I'm a bit puzzled by こともありました at the end of this paragraph. At first I assumed that the company who bought 18 million Yen of coupons were the people who bought the boat, because the clause are joined with て. But the こともありました ending makes it sound to me like the boat buying was a separate thing.
Is there some aspect of こともありました that I'm missing or are these two events unrelated (even though they are joined with て)?