They were/are required to provide you a complete copy of the trust. Did they send you a copy? Demand a copy in writing under 16061.5. I'm assuming your mom lived in california
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Assuming that your mother lived in California, you would still receive the notice even if you were disinherited prior to your mother's death. As Mr. Shultz indicated, you are entitled to request a copy of the terms of the Trust. If the Trustee did not provide a copy at the time the notification was sent, then request a copy. All beneficiaries and all heirs - whether or not they are a beneficiary (an heir is someone who would inherit if the decedent did not have an estate plan and as a child of your parents you are an heir of each of your parents) are entitled to the notification.
Please obtain a copy of the trust and if you have any questions about what it says then contact an attorney.
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Yep, you're an interested party as an heir, so you'd get notice even if you weren't a beneficiary. You should determine whether there was a pour-over will associated with the trust. If there wasn't, then there might be assets in the estate that aren't in the trust, and you could be entitled to your intestate share of those.