Billed for a return Job

I took I'm my car for 599, 69 point check and and engine overall job diagnosed by them. I agreed that it must be done. I was then invoiced 15000 for it(with a 6month Guarantee@the bottom of the slip) . I paid it which it took them 1month to sort it out after I urged them... I receive the car 1month late I drive it for 2days, in doubt... I them notice Oil in the water tank/radiator and a cracking sound from the engine I called them and told to bring it in. On the way to them the car siezed. I then left the car on the side of the road and went to them in ormonde. They don't tow but pull my car to their garage. I later get a call telling me that its my radiator@falt but they\l fix it 4days later I got a bill of 12000 telling and of 5000for radiator and telling me that they won't fix it till I'm willing to pay the bill."