Did you take out a subscription with the one month free trial? If so, you should still have access to premium and it may just be that you logged in with the wrong details. Check the email receipt from Spotify which will show the user name you should be using. If it's a 10 digit number, you need to log in with facebook.
If you had the 7 day mobile trial, I suspect it ended when you reset your mobile but you can still go for the one month premium trial when you subscribe.