They can be low for a single person but get easier the more children there are. Speak to your IP about a reduction if you are struggling or perhaps consider bankruptcy and check to see if you would be better off with the official receiver's guidelines.
There are guidelines produced by Stepchange and other organisations. If you want the Stepchange ones you can email me and I will send them to you. You can then see if you are getting the right allowances and if not take it up with your IP.