If its been in the same pot for 8 years, its likely time to pot on, rather than repot - get a bigger pot, that means, adding new ericaceous compost, but you might just inspect the plant thoroughly first, looking for signs of infestation or disease - soft spots, scale, mealybug, rotting areas near the base and so on.

This is difficult to troubleshoot without a photo. Orange trees need 6-8 hours of direct sunlight per day and are extremely hungry & thirsty plants. Those pots are often a deathtrap for plants as they mature. They are not very forgiving. Is it deprived of sufficient sunlight? water? food?

It could also be an infestation either above or below the surface. Is the bare twiggy growth still green or like dry kindling?