hey!
Gosh that does sound disorganised
I guess the only way you would get it sorted is:
1) make a complaint
2) get your classmates and all of you complain to either - form tutor / head of department/ head of year / headteacher / or student union... (ours haven't achieved anything yet apart from make admin unblock facebook and snapchat, but have reblocked the student room...
) but you could always complain to them or set up a petition if other students also have no teachers...
3) get your parents involved
I would ask your teacher to email you the PowerPoint(s) you would have been using in lessons, really they should be emailing the students they are teaching to let them know they are going to be a no-show, so then you don't have to waste your time going to an empty classroom - especially if they are cancelling them.
mind if I ask which year you're in & how long has this been going on for? The tutors get paid for you to get the best grades you can get at AS/A Level, although you could also argue you are meant to be independently studying for them... On the other hand, there have been A LOT of colds going round lately - all of our teachers at our sixth form have got them!!
I would suggest downloading the specification for each subject which you are doing, and printing it off. There you will be able to see which topics you are doing. Perhaps during your large free lesson gap, you should go to your sixth forms library and plan your own lessons so at least you won't fall behind in the mean time?