Definitely nursing strike as it happens around 12 weeks . Keep putting baby on breast and try and pump every 2 hours .
My son had nursing strikes due to mastatis and it ended up lasting until he was around 6 months old because i kept putting pressure on him to feed due to weight. Have you tried offering feeding when they are sleepy or dream feeding because they are more likely to take the feed then.
Oh that sounds so stressful I'm sorry. Firstly, pumping isn't an indication of supply. Your baby is much better at getting milk from you then a pump or gand expressing ever will be. Are they still producing plenty wet and dirty nappies. In the days leading up to this we're they still coming off the breast happy and satisfied? Just thinking it may be a nursing strike