Randomly got a refund on Amazon that I didn't request

Hello all,

To explain the situation:

I ordered a basket of roughly £400 worth of pc parts, as well as a watch on Amazon with my credit card, around 2 weeks ago. Every item except the watch was sold and dispatched by Amazon, and was delivered the next day with prime, and the watch was sold by a third party store so would take a week to arrive, not a problem. Everything went through, £400 was gone from my account, and I received my items (except the watch). After my other items arrived, I had a look on my Amazon orders page, and all items showed delivered, except the watch which asked me to reverify payment method. A bit strange I thought, but I proceeded to try to do so, at which point it asked me to verify through my banking app a transaction of £400 (the original cost of my basket which included the items I had already received). I clicked out of it since this money was already gone and I didn't want to pay again. Somehow this "worked" to verify my payment method as I got my delivery date back for the watch. Now, 7 days later, my Amazon orders page shows the watch as cancelled, and my £400 transaction has been refunded. All the other items I physically already received just say "Delivered"

No emails or anything from Amazon, how likely are they to chase this up? I'm happy to pay as I'm not a thief but don't wanna be a tit and go contacting support to pay when I've practically been gifted £400 by them

In England