Bought Complete Edition but didn't get all the DLCs (Steam)

Hello! I bought a Dredge Complete Edition in Steam, and I was thinking it would give me the game and all the DLCs. However, it turns out I didn't get all the DLCs.

I am still missing the Custom Rod DLC. I assume it is an error, so could you tell me who should I contact in order to get a missing DLC, please?

UPD: I understand that the Custom Rod DLC was initially a pre-order bonus for Dredge. However, it's common for pre-order bonuses to become available to the broader audience after some time, often through a "Game of the Year Edition" or "Complete Edition." Allowing early adopters to enjoy exclusive content is fair, but it raises a question: why keep such content locked away artificially, especially when more than a year has passed since the game's release? Releasing it later could benefit both new players and loyal fans who missed the pre-order window.