Was it acceptable for my teacher to do this?

I'm in year 12 at school and we have been made to go back to school after completing our AS levels in order to supposedly start the A2 course. However this hasn't really happened and we have literally been doing sod all in most lessons. It's got to the extent where I'm being made to go into school for one lesson in an entire day. Now, when I turned up to one of my English lessons my teacher asked us if we wanted to make a collage using a magazine and a few colouring pencils. I was like WTF this is an English lesson not an art lesson for preschoolers. So instead she got us to sit round the computer watching her buy art equipment on ebay for another lower school lesson. To me this just seems wrong. I know it's the end of term but to me this is so unprofessional- it seems like she can't be bothered to teach us. Also my geography teacher forgot to turn up to one of our lessons and then he claimed he was engrossed in reading a book about rocks! My parents actually complained to my head of year, not about these specific incidents but generally about what a waste of time school has been. When he replies he claims that my teachers have said that I have not engaged in their lessons and that I have not had the initiative to catch up on work I've missed. It's like what work?! I don't think I'm being unreasonable here. I'm an incredibly hard working student who puts 110% into everything and I feel pretty hurt that my teachers turn on me just because they're being criticised. I love all my teachers but still I feel that some of this behaviour was just slightly disgraceful considering my parents are paying an awful lot of money to send me to that school. What do you think? Was my teacher wrong to buy things on the internet during a lesson? Please don't make rude comments- believe me this is not the only time teachers have done stuff like this! Thanks for reading :)