Just made another 7 day trial (about 10 days after the first one ended) and it worked first try.
1. I have a dynamic IP address, and have unplugged my router once since making the first account
2. I used a firefox incognito window
3. I used the firefox extension CanvasBlocker (make sure you allow it to run in incognito mode)
4. I made a fresh recu account with a throwaway mail service
5. I confirmed the email address in the email they send you
6. I logged in to the recu account, went to 'My Account', hit 'upgrade' for 'current plan', and clicked 'get' for premium (center option)
Things I would check if it's not working for you:
1. IP address, it's almost certainly going to be that your IP address has already been used to make a trial. Check your IP address and then try to change it. Remember that sometimes even VPN addresses and mobile addresses will have already been used. If you don't know whether you have a dynamic IP address or don't know how to change it, GOOGLE HOW TO DO IT, it is not complicated.
2. Double check that CanvasBlocker is enabled for incognito mode and currently running, if you don't know how to enable an extension to work in incognito mode, GOOGLE HOW TO DO IT, it is not complicated.