Am I going to get kicked out because my rent was late???

I've paid my rent on-time, in full every month for 18 months! Our apartment has started doing this weird thing where they put our rent online on the 26th, but don't put our utilities online until the 1st. It's an extra charge to use your debit card, so I planned to pay them both on the first. But then I lost my debit card, I used my credit card (or so I thought) but apparently it didn't go through. I thought my rent was paid, but it wasn't.

Today I came home to a letter that says "Notice to Vacate" on my counter that says I have to be out by March 6th! I rushed online and checked and paid the rent. Is there anything I can do? I didn't see it until the rental office was closed. I can't stop crying. I don't want to leave. In fact, I accidentally paid twice the amount I was supposed to. But that's fine because I really want to stay.

Is there anything I can do?

It says at the bottom that "this notice to vacate is unconditional." What does that mean?