On 22 of Luly i send £1.800 in Bitcoin to Blockchain.com. Did not touch it or check for about 3 weeks and when 12 of August I login to my account I noticed that on 9 of August my money was send to another wallets in 2 transactions.
Correct me if I'm wrong but I am wondering why you sent BTC in your blockchain.com account without even bothering to check it if it was sent successfully or not which I assume is the ideal thing to do no matter how small or big the amount of your fund being transferred.
I think a simple check from a blockchain explorer at your intended recipient address would be enough to confirm right away that your funds were sent successfully. Imho.