Do Not Disturb Feature Not Working

So- I am not sure what is going on with my phone. Apple said it offers a fantastic feature called “Do Not Disturb”. However it does not work. I’m receiving back-to-back spam phone calls repeatedly and triple checked settings to confirm the DND is in fact set to “On”. I’m considering leaving iPhone altogether. The Company is not same quality as it was before and it’s inconsistency is giving me whiplash.