hair won't curl!

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So I have a few issues when I'm curling my hair. Btw it's quite and dyed.
1) the curls never stay in! I don't get it! I use heat protection, hold for as long as poss do it curls, I hold it after and use hairspray! My hairdresser curls it and uses hairspray but they stay in??
2) I curl my hair with straighteners as I've found its the best method for the curls I like. However it's very picky. Sometimes it won't curl at all and others it'll be like one huge chunk of hair that doesnt! It's so frustrating especially in a rush...
Any tips to help? Xx