Womens Wimbledon Outright Market Help

In need of some help, I've placed the following bets on the Womens Wimbledon outrights;

Wozniacki £10

Serena £8.75

Pironkova £1

Sharapova £6.75 @5.4

Azarenka £4 @ 12

Total red on all other players = £30.50

Wozniacki, Serena and Pironkova have all been eliminated. Sharapova and Azarenka remain. My red on the other 2 semi finalists was -£30.50.

I have layed of Sharapova (Backers stake of £16 @ 2.32) and Azarenka (£10 @ 4.9) and now have a red on the remaining 4 players of about £4.50, the biggest red being £5.50.

By my logic I should have £25 returned to my balance, but I do not. I have had about £10 returned to my balance??

Please can somebody advise/ explain.