Eviction Notice!

Okay so I live in government housing, so it’s based on my income. I live with my fiancé, my mom, and my 4 month old son. Our rent (including all our incomes) has been 160$ a month. My mom wasn’t working, so she would babysit while I’m in school and my fiancé and I are working. We’ve been here for about 5 months and nothing has changed. But, we got a letter under our door stating that our rent (which was due nov. 10th, but we were a little late because we had to wait on pay day) had been raised to 450$. And it proceeded to say that if we did not pay the 450$ by nov. 27th, the manager would start the eviction process. We’ve never been late on our rent until this one time. But the letter was dated for nov. 13th, so AFTER our rent was already due. But we didn’t even get the letter until we were about to drop the money order in his mailbox on nov. 15th. So my question is, can he raise our rent AFTER rent is due for the month but still expect us to pay it that same month? And can he give us such little notice? I always thought he would have to raise our rent at least a month in advance. So we should have been able to pay the 160$ this month and start at 450$ next month. I’m also unsure why our rent is being raised so much when nothing has changed. We’ve tried to contact the manager several times but he’s out of town until the 27th (the day we owe the 450$). Is this legal? I’m not sure how to get ahold of corporate or whoever is over his head. Any advice?