My parents won't believe me that we have mice/rats?

I'm a 17 year old girl, and my parents won't believe that we have mice/rats in the walls. I hear them squeaking and scurrying, tapping and pitter-pattering in the walls. It's absolutely horrible. I'm very sick all the time, so I have to stay home from school, and I hear them all day. Of course, my parents say I'm imagining the noises because THEY can't hear them (because my parents are incredibly loud, while I'm very quiet and often bedridden). Apart from being sick, I have horrible anxiety disorder, and I'm going mad thinking about these horrible mice and rats in my walls, just waiting to come and infect me more, give us fleas and ticks and horrible things.

At my old house we had hundred of mice because my parents refused to believe an infestation was starting, and then once they realised it was happening, it was too late. They are too cheap to call an exterminator, and won't let me use my christmas money to get one here. I called one the other day, inquiring about an estimate and asking her opinion, and she said although it could be the pipes (which it's not) from my description it sounds 100% like mice, especially given the season.

What can I do to convince my parents I'm not crazy, I'm not hearing noises, and that our house has mice or worse, rats? I have to live with these things every day, I can't escape them, and I'm absolutely petrified :( I'm so worried it's making me sicker. I cry every single day.