no hot water ?

i get no hot water or if i do get hot water it for a few seconds then goes freezing cold ,if the cold tap is put on hot goes cold straight away and that is if i have heating on or off ! we moved into the house oct and had two new parts added to it as wouldnt even come on ! it takes an hour to pour a bath i,m sick of it . the council think im lying and have now said if i phone once more im getting charged ! the council say that if i have the heating on i get no hot water and viceverca even when my washing machines on i get nothing please help as one of the boss's coming out thursday and i need ammo !