When you say they don’t work, what exactly do you mean? Are you getting zero watts or is it that the values are not what you expect?
Can you verify that these are stereo or mono extensions and not four conductor?
Have you verified that the plugs are fully seated on both ends?
I ask these questions because I have tested quite a few of these and never had even one fail to produce results.
UPDATE: Searched back and this source has quality extensions for very reasonable prices. I have tested:
G5212846 - 6"
G7448384 - 6’
G7561845 - 12’
G7577902 - 25’
These are well made utilitarian cords. I find that Amazon and others are typically catering to the audiophile community with gold plating and color/texture schemes that have little to do with functionality but exploit the whims of those with disposable income.