Well, I did a week ago a hard reset on my Lumia 625 just to start fresh with it and install for the last time all apps I'll use on the phone before the Store goes down. And I didn't know I can no longer sign in with my account.
Hi!
So did I with a Lumia 640 LTE with Win8.1 Update2 on Nov 14. Since then I get the famous message "... Try again later" etc when I want to sign in to MS account. November 14 to 21... Exactly same time, two other Lumia phones of my family can't load "my apps" section in Store with c101a006 error, another celebrity. From later to later I think we'll not be able to sign in or install some apps. Ever.
In time, I saw too many... bizarre (in)decisions from MS and I'm not so optimistic, sorry. In short, I believe MS has close the Store one month in advance, in fact. MS has a whole history of controversions (the gentle term) behind.
It is my opinion and I'll be glad if I am wrong. We'll see. December 15 is coming in three weeks.
I was also facing the same situation but finaly success to login in 1020 do one thing in mid night aroud 3am try to login on account and i am dam sure it will be login
Good luck !