Don't hesitate in making a formal complaint. The provider you are seeing should have a complaints procedure that you can follow. Chances are the jobcentre themselves won't do anything unless the provider doesn't respond to the complaint; the jobcentre don't hold their contractors to particularly high standards.
If a formal complaint doesn't get you anywhere, then I'd seriously ask why you are bothering with the scheme in the first place. Work Choice is optional so you should be able to leave. Its no good staying on the scheme 'just in case' someone might be helpful, when all it is doing is making you stressed.