Hey @Pigeonjock69 and welcome to the Community!
Which bonus are we exactly talking about? If you are referring to the welcome offer used in November, here's why:
"-If your Racing bet wins, you have completed the bonus, you receive your winnings and your stake.
-If your Racing bet loses, you will receive your stake back up to a maximum of £40."
You did place a qualifying bet of £10 but it was a winning one, hence bonus is marked as completed.
Let me know if it was not this one and I can check it further.