I dont mean to be rude, and I do understand your situation because I am also struggling to pay bills, but a lot of FT workers who dont claim benefits have also lost similar amounts of money, due to the current cost of livng, and nobody cares a damn about them.
A good friend of mine who works FT as a nurse, last winter couldnt afford to turn her heating on or pay her council tax. She is currently facing court action. She is dreading this winter. She has 2 young kids. Yet your complaining that your benefits, a luxury you get from tax payers, from, workers who are also struggling to pay their bills, has been cut. You probally earn more money than a lot of people do working FT. Me personally would love to have £50 spare a month to have as "pocket money". Im lucky if I break evan.
As people above have suggested, your son needs to get a job. My 18 year old son is currently in a FT university course and working 30 hours a week in a pub. He understands life is expensive, and to fund it he needs to earn his keep. My 16 year old daughter also has a PT job to fit around her schooling, as does most of her friends. You could also get a PT job. You state you share your children 50/50 with your ex. The 50% of time you dont have them, you could work. Yes its hard, yes you dont have any time to yourself, but how do you think other parents manage ?. Children copy their parents, if they see you not working and getting paid the privilage of doing so, they will as well. Set them an example
In a few years time, all your children will be grown up. Your benefits will stop. Your children will more than likely move out. You will be left alone with no job, no benefits and an empty house, what will you do then ?