Go to bunnings and get one of these, one of the best tools you can have in your tool collection. It'll help get that stubborn clamp off, then once off throw that clamp in the bin and get some proper worm drive clamps, better for tightening and dont cut the hose.
Then its just a matter of getting your hands cut, bit of swearing and then some struggling. With the new hose put a bit of vaseline in the end to make it slip on easier