Import Contacts creating dupes despite dedupe rules
Easiest way is just to use the Contact ID if it is in your file.

Are you importing to the same location type? It does not dedupe a given data point if importing on a different location type.

I've noticed that you must set your desired dedupe rule to be unsupervised. Selecting a rule that is not marked unsupervised hasn't worked lately and is probably a bug.

I believe this is related Import Contacts with dedupe rules