I need to print a mailing label to return my old modem

Every time I submit the form to request the mailing label, it takes me to a page that says "Sorry, this isn't working right now" and says to try again later.   Then when I get back to the website's home page (or any page), it says "400 Bad Request cookie too large"...something like that.   I did research and found that I needed to clear my cache and delete cookies.  I did that.  I restarted my computer.   Same things happens.   I've been trying to get to the mailing label for over two weeks now.  If I don't get this returned, they are going to charge me.   It is so hard to get to a real person on the chat.  It just takes me in circles.   This is making me want to cancel my service and find another company to get my internet from.