cut the nail varnish pot in half or send it to the manufacturer and say due to a design fault I can only get half of the product out of the bottle I alway use your products and I'm disgusted at this...they will probably be so socked by the cheek of it they'll send you a new 1. Or just buy a nail polish brush from Virgin cosmetics they are usually quite lon, you know the tester ones that might help.
Put boiling water into a cup and place the nail varnish bottle into it for a minute. only do this with nail varnish in a glass bottle and make sure the bottle is shut.