Decomposers act in which level of the trophies pyramid?

They are the "last trophic level" in some hierarchies because they feed on everything (National Geographic). However, according to the strict trophic level definition they would be primary consumers

Decomposeds act on the last trophie level.

Explanation:

A separate trophic level, the decomposers or transformers, consists of organisms such as bacteria and fungi that break down dead organisms and waste materials into nutrients usable by the producers.