Storm-chasing contractors and insurance claims
The universal rule is that if the vendor solicits you instead of the other way 'round, he has stacked the deck in his favor at your expense. Either in cost or quality. This is what you pay for the convenience. 

If you signed papers then it sounds like the negotiation phase ended. 

Your next step is to read the papers you did sign, and see what you are allowed to do, and what you are obliged to do. 

We can't guess because we didn't read them either :)

In the future, never, ever, ever, ever, ever hire a company you learn about because they solicited you.  You are welcome to say "Get off my property" then use it as a tickler to remind you to do your own self-initiated search for respectable roofing vendors.  Also beware of social media which is easily faked like Facebook, or in the business of referrals like Angie's List.  Yelp tends to be full of salty gripers, but it's actually not half bad for this, because they really work to keep corruption/fake reviews off. 

Also in the future, read before you sign (recommended: never sign the same day). Most people believe "keeping your word" is a cornerstone social value, essential to honesty.  Well, think about it, how can you keep your word if you don't know what your word is?