We've been asked to suddenly pay $16k in 11 days?

We are not sure what's going on but it seems that our roommate entrusted with paying rent might not have done so. We moved in in August, yet suddenly we get a note last night demanding rent from august last year to January this year totalling 16k and we have 11 days to pay it. We never got a warning about this, no other letter or call or anything warning us that we were falling behind on rent. Can they really do this so suddenly? we want to work with the landlord to pay the back rent but definitely cannot do so for such a large amount in 11 days. This is stuyvesant town btw. ANy advice? thatnk you