You've applied your label to a smooth, plastic surface, and for whatever reason, it just won't stay put. This scenario is not uncommon. An interesting phenomenon sometimes occurs when applying labels to low surface energy (LSE) surfaces like plastic: labels just won't stick.
If you could look through a microscope, you would see oils from the plastic substrate left over from the manufacturing process. These oils interfere with the label adhesive's ability to grab to the surface of the plastic. That's why cleaning the surface with alcohol won't do the trick.
Instead, treat the surface with a corona or open flame. The flame will evaporate any surface oils. It will also microscopically roughen the surface, allowing the label to stick.
Of course, there are also particular LSE adhesives that work well on plastic surfaces. Request an LSE adhesive the next time you place an order for labels intended for plastic surfaces.