Budget insurance car hirer

My car was on repairs since first week of January and budget hired a car for 30 days for me. Now my car its still not done and they can't even tell me how long it will take as the repair still waiting on parts. The car hirer i had to take it back because it was due and when i ask budget they told me that they can't extend the hired car i must pay to extend but they don't even know how long i must wait to get my car back. I would like to know why they don't hirer a car until i get mine back.