If there was a 'first deposit only' bonus, then the message wouldn't appear on the deposit page after the bonus has been claimed.
The first deposit bonus was claimed, yet the message is still there each time.
Nothing more to it.
Not even trying to imply or deceive here.
If they don't intend to give a bonus, then remove this message.
OK, then I believe as a responsible user of the casino/service, you should inform them that there's something wrong with their "first deposit" bonus page/panel/dashboard instead of taking advantage of it. It's obvious that it isn't what they intended, and if they won't give you the bonuses after your first bonus was claimed, you start a topic to tell everyone that they're scamming you?