I get those too. Note that nowhere does it claim the amount you paid in is your
balance. Your benefits won't go up if you retire at 100 years old. Your benefits won't run out if you live to 500. It's not like a 401(k) or IRA, where you have $x dollars in it that's
your money and have to budget your withdrawals.
They won't update the "amount you will get" to reflect Congress dipping into the fund. The statements operate on the "if everything continues to go well" basis, and so what Congress does isn't reflected on them. No one gets their next statement and asks "hey, where'd my money go?"
That's why it's politically safe to raid, at least in the short term.