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Please don't mark this as a duplicate question, as I have found similar questions on what to do, but not the best way of how to go about doing it.

I accepted a job offer from Company A. I signed the contract. Legally, this isn't an issue since both the state and contract are employment-at-will on both ends.

Since signing, I have received an offer from Company B. I believe that the job at Company B would be much more interesting, that Company B would value me more as an employee in an abstract/personal sense, and that they do value me more in a concrete sense considering the salary is 33%-38% higher than the job at Company A.

The only questions I've seen on this are what to do here/the consequences of the decision. I have already made up my mind to revoke my employment at A and work at B. I am aware of reputation related consequences, but don't consider it an issue since I don't intend to apply to A in the future again, and the companies are in different industries and are in different states.

My question is, how do I go about doing this with respect to Company A? Do I call the hiring manager? Call HR? Is an email ok? (That seems like a very awkward phone call, especially considering I originally declined Company A's offer and then called them back 2 days later to ask to get the offer re-instated, which they were willing to do.) Or do I just go rogue and ghost them?

Technically speaking, are there really any consequences of ghosting?

I know that it isn't the best thing to do in general, and ghosting in particular. But this comes after 10 straight months of spending almost all of my free time searching, applying, and interviewing for jobs. This would be my second job since graduating. I need this, and the process has been cut-throat, so it's time for me to be cut-throat.

Thanks for any help.