Cistern wont stop flushing!?

I have a concealed cistern with a front mounted dual flush cable mechanism wich has been gradually getting longer and longer to stop flushing.
It is only 6 months old so should not need new parts.
It is difficult to get into the cistern because there is a worktop over it.
Ican remove the front panel which then has a cable mechanism connected.
How do I disconnect it and how dificult is it to mend?