Universal Credit Complaints

Not sure quite how to put this, but, can anyone advise how to successfully complain about UC staff etc - they just get worse, if you can actually get hold of anybody
btw my MP option is no go
Have tried most if not all complaint methods and no response, especially that online fill in the box thing, that goes straight into cyberspace, never to be seen again
If you use main phone number you get an arrogant **** who spiels off lies and then usually cuts you off
Written several letters, still not heard anything
Email, tried that too - no response
Journal thing usually ignored too, or very delayed response, then fobbed off with more lies
Anyone had any successful responses ? do tell