I am unable to set up my mobile phone to send texts to Twitter!

I recently opened a Twitter account, went to "Settings", then "Mobile" and entered my phone number in. Twitter prompted a code I needed to text in from my cell. I text the code to 40404, and nothing happened. I reset the code several times, and still.... nothing. I logged in a couple of days later to see if the problem was repaired, and my moblie page is permanetly stuck on "Use Twitter with Text Messaging" send the word START to 40404... I have sent start several times now and again, nothing! And now, I can't even get the page to reset itself so that i can try reentering my phone again. I'm highly frustrated at this point. Any suggestions?

Yes, my phone is set up to text to short codes; that isn't the problem.