I understand your frustration. And thank you for the warning. However, we can't blame Coinbase for what happened to you. Based on your own story, it seems like you got hacked. Either because you didn't secured your stuff, or someone was very very smart. However, either way was the case, what do you think Coinbase can do about it? How is this their foul?
I am so sorry for what happened to you. I believe your gmail was the problem... and you didn't have two factor authentication on your coinbase account. They didn't swap your sim...they simple gained access to your gmail and used it to recover your coinbase pass.
Im sorry!
RE: If you have a Coinbase account: BEWARE because you could lose everything you own, just like I did (help me spread the word fellow steemians!)