Apps using the CallKit call-blocking or identification extension, or the SMS and MMS fraud-filtering extension, need to genuinely serve their stated anti-spam purpose — using them to insert unwanted call or message behavior is a direct violation.
Rare, but comes up when a caller-ID app's blocking-list logic is inverted or manipulated in a way that looks like it enables, rather than prevents, spam calls.
"Your app's Call Directory extension does not function as expected to block or identify spam calls, per guideline 2.5.12."