how can i fix my gas hob, Alto parkinson cowan?

my gas hob burner's appear to be blocked i am left with one burner working properly and one semi working and two that do nothing, i was cleaning it recently makeing the problem worse as the semi one that did work is now no longer throwing the flame like it did before and no sound of gas comeing threw, so i took the lid and plate off and tried clearing the little whole where the gas comes threw thinking this was blocked, i have tried leaving it alight for a bit and the flame goes higher but still no sound of gas and when i put the outer plate and lid back on the flickerig sound starts and the flame is barely there can any advice be given to help me sort it thanks.