Octomom: Pay Up or Get Out!

The man who holds the note to Octomom's house says he's fed up with her empty promises, and now wants her to pay $450,000 plus interest by New Year's Eve ... or get the hell out.

Amer Haddadin says he's been plenty understanding when Nadya Suleman fell behind in making her monthly payments. A $450,000 balloon payment has been looming over Octo for months -- it becomes due every time she falls behind in making payments.

But Amer says she's fallen behind again and now he's had it. So Amer tells TMZ he just served Octo's lawyer with a letter demanding she pay the full $450,000 balance plus interest by December 31 or get out of her La Habra home.

Octo has been saying for months ... she's broke.