Sadly I'm now affected by this issue as well. I cancelled my payments in February as I was not going to be able to play for a month. I tried to add the same credit card I used since August (many times) 2 days ago and keep getting the 406 error code.

Has anyone had this issue resolved after contacting SE? I now have 15-18 transactions on my credit card of $1.10 each. Has anyone successfully had these charges reversed by SE?