Controller don't run!

[eluser]Unknown[/eluser]
Hi!

I got a controller which will update a database if a customer has paid or not!
I am using Payson to do this. and payson will send back post data to site (controller) where it will say if the payment worked or not. and if it worked it would update the database.

THE PROBLEM:
I have set payson to send those data to a controller: www.site.se/paying/payson.
but that controller never runs, so nothing happeneds, and I know that because I was trying to create a file(fil_put_contents(); to see if it worked but it didn't.

WORKS:
But! It works if I set payson to send the data to a file without the codeigniter framework; a normal file.php.
So codeigniter make this unworkable.

Can you please tell me your idéa about why this may not work! guess or something!

Thanks in advance =)