I'm Lucy, and I'd be happy to answer your questions today. I'm sorry to hear that this happened.
Police have immunity from lawsuits from issues that arise while doing their jobs except where there is a civil rights violation, and this unfortunately does not rise to that level. When there is a dispute between two people living in the same property, police can help calm the dispute and remove someone temporarily from the premises, which is what they did. They don't have the authority to take testimony, hear evidence, and decide who has a right to be on the premises. That's a judge's job. This is why they told you it's not a police matter. In order to regain access to the property to get the rest of your stuff, it's necessary to get a court order directed at your former girlfriend.
You can sue her for breach of contract, even without a written lease, as long as you were staying there with her consent. You still have a valid month-to-month tenancy. Damages include the cost of you staying elsewhere for up to 30 days. You also have a right to seek a court order granting you two months living in the property, or the equivalent of the rent for two months, plus attorney's fees. Hawaii Rev. Stat., Section 521-63. You're also allowed to file for conversion, making that you're asking the judge to order her to pay you the reasonable value of any of your belongings that you weren't able to take with you.
To start, try talking to some landlord/tenant attorneys in your area. They're the ones with the knowledge and ability to help fix this for you.
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