Touching the ball twice

Hi coach,

The other day while playing a doubles match, one of opponents hit the ball twice (actually the ball hit the two different part of his bat very rapidly while swinging once)and the ball bounced on my side of the table. He said that it was illegal to hit the ball twice, so he said that he lost the point. But I said that it is legal to hit the ball twice accidentally.

Such a rare accident happened to me once or twice in the past during some matches.

Is it legal to hit the ball twice accidentally?