Basically the other day I was late for school and it wasn't my fault so my mum said not too worry she will ring up the school so I don't have to go. So of course I didn't go. Now I got an hour detention, after school for failure to attend although my mum rung up. Can school force me to stay for detention withot parental consent? Especially since I actually don't deserve this detention considering I have never had an hour detention in my life and this is my last year.

Deserving detention isn't based on the fact you never had detention.
Your mother should have sent a note with you when you went back.
Detention for a day off school that was determined by your mother and she called doesn't seem like they should have given you detention.
What do their actual rules state about days off and late days?
Really you should not be taking a day off to get out of being late, but I have been there myself. Some times the way they have the rules written up its better to take a day off than consequences of being late. I never could figure that out, but is that the case with what happened with you?

If the school rules are being applied consistently there is nothing you can do about it. Disciplinary actions in school are not covered by civil law except in terms of corporal punishment.

Deserving detention isn't based on the fact you never had detention.
Your mother should have sent a note with you when you went back.
Detention for a day off school that was determined by your mother and she called doesn't seem like they should have given you detention.
What do their actual rules state about days off and late days?
Really you should not be taking a day off to get out of being late, but I have been there myself. Some times the way they have the rules written up its better to take a day off than consequences of being late. I never could figure that out, but is that the case with what happened with you?

Im not taking the day off I never did.

So of course I didn't go.

The fact is you didn't attend school that day. My guess is the school did not accept your mum's reasons for holding you out of school and that's why they gave you detention.

You are asking if the law allows the school to do this and the answer is yes. So accept your punishment and move on.