SM-G925W8, I tried flash custom rom and now my phone won't boot. HELP

SM-G925W8, I tried flash custom rom and now my phone won't boot. HELP. I can't access download mode I all methods I simply can't access it but I can access recovery mode and use adb side load. How do I flash stock rom?? I tried and it won't let me.. fast boot won't work. I can't access anything except the recovery mode. I have tried wipe cache and factory reset.. won't work!! help!

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