Block 10 has sold out. Block 11 has 137 left as of 10:20. With blocks 9 & 8 yet to go on sale (or haven’t gone on sale online at least) - so probably more than half of the allocation available.
The middle of block 113 is the gangway and entry. So half of the block to the left of the gangway with the ‘L’ is 113 then half of the block to the right with ‘E’ is also 113.
If you can’t get in at Stanmore, pop down to Canons Park which is the next stop down the line. Car park is also large and never seems to be as busy as Stanmore whenever I’ve gone down.
Have you just created the account for the additional ID? Its possible SWFC aren’t allowing newly set up accounts (or since a set date) to purchase tickets, even though they’ve not said this anywhere.