Coinbase Wallet hacked

I had my Coinbase Wallet was drained yesterday of all my crypto totalling c£70,000.

Coinbase are 'investigating' but saying as it's a self custodial wallet little likely they can do.

This is despite fact that my 12 word seed phrase I have memorised and it was only written down once on a single piece of paper which was immediately locked in a safe that only I have access to the keys for. I'm fully aware of my responsibilities in keeping the seed phrase secure. And did so.

So how on earth can my wallet be hacked unless the Coinbase Wallet app is compromised?

I advise anyone using Coinbase Wallet to IMMEDIATELY move your coins to an off line cold storage device or similar.

I've been sooooo careful with my CB wallet seed phrase, as I say committing it to memory. How can this happen? It's pretty much my life savings....stolen it seems.