What you said
As an NQT, you're not supposed to be exposed to unusually difficult classes. You can plough on and try to crack their behaviour by any means necessary, but get your head of department, mentor, head of year and senior leadership team on board so that they can't hold it against you if it all goes pear-shaped. Or demand your rights as an NQT and get assigned to an alternative class - and contact the local authority as it is likely to be supportive.
Why not approach a member of the senior leadership team and ask for a meeting as your mentor is off sick? Lay your cards on the table and ask for support. If you are proactive in this way the response will be far better than if you allow the situation to remain as it is. Your head of department is also there to help.
The expert view
The problem is not with you but with the pupils' behaviour and the school's inability to support your efforts to amend it. Keep setting detentions. Keep your paperwork immaculate; record who, when, why. Then follow the school's behaviour policy to a T. Request that line managers assist you as the behaviour policy dictates. If they don't, politely ask why. Keep the pressure up on those responsible for assisting you. Make it easier to help you than ignore you. But keep doing it: the certainty of a sanction is more important than its severity. The children have to know you mean business and the school has to support you in getting that across. If your colleagues don't support you, they don't deserve to have you and you should look for a better school.
Tom Bennett's latest book, Teacher, is published by Continuum. Read more from Tom on his TES blog, or follow him on Twitter at @tesBehaviour. Post your questions at www.tes.co.ukbehaviour.