Amazon started adding promos (ads) for some of their original content at the beginning of playback a while ago, but that's all I've seen there. I rarely use Netflix, so can't say I've seen anything there.
Are you talking full blown ads for something other than what they both offer. or are they just internal promos? Are the interrupting a playing video with an ad? I would be extremely upset with the latter, and don't care for but can ignore their internal promos.
This is something that you need to contact Netflix/Amazon about. Roku doesn't have any control over what's shown within another provider's channel.
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