Elohim/God says That The only Authority on matters of Law is the Law of Moses in the Hebrew Bible. This is what Elohim/God has taught me. Elohim/God has shown Jewish Karaites this same perspective of the Law of Moses Being the only Authority on matters of Law. Evidently, Elohim/God has shown you something different.
Well, the biblical text does say
and thou shalt come
to the priests the Levites, and to the judge that shall be in those days, and inquire; and
they shall tell thee the sentence of judgment:
וְעָשִׂ֗יתָ עַל־פִּ֤י הַדָּבָר֙ אֲשֶׁ֣ר יַגִּ֣ידֽוּ לְךָ֔ מִן־הַמָּק֣וֹם הַה֔וּא אֲשֶׁ֖ר יִבְחַ֣ר יְהֹוָ֑ה וְשָׁמַרְתָּ֣ לַעֲשׂ֔וֹת כְּכֹ֖ל אֲשֶׁ֥ר יוֹרֽוּךָ׃
and
thou shalt do according to the sentence, which they of that place which the Lord shall choose shall tell thee; and thou shalt observe to do according to all that they inform thee:
עַל־פִּ֨י הַתּוֹרָ֜ה אֲשֶׁ֣ר יוֹר֗וּךָ וְעַל־הַמִּשְׁפָּ֛ט אֲשֶׁר־יֹאמְר֥וּ לְךָ֖ תַּעֲשֶׂ֑ה לֹ֣א תָס֗וּר מִן־הַדָּבָ֛ר אֲשֶׁר־יַגִּ֥ידֽוּ לְךָ֖ יָמִ֥ין וּשְׂמֹֽאל׃
according to the sentence of the Tora which they shall teach thee,
and according to the judgment which they shall tell thee, thou shalt do: thou shalt not deviate from the sentence which they shall tell thee, to the right hand, or to the left.