First of all, your temps sound too cold to me. I keep the warm side of my tanks around 85*-90*F. The cool side of the tank should be around 75*-80*. I use an under tank heater on the warm side only, and keep my tanks in a warmer room where there are no drafts. Make sure to measure temps. at the level of the sub-straight, since this will be where the gecko will be hanging out. I would warm the warm side of your tank up as soon as you can. If the temps are too cool, they can't digest their food correctly. It's the most common reason why they will stop eating.
For hides - it's best to have a warm hide, a cool hide, and a humid hide. The warm and cool hides are easy to figure out - one on the warm side of the cage and one on the cooler side. The humid hide is to help with shedding. You can use whatever for the hide, but then put in some moist moss or coconut fiber or damp paper towel. The higher humidity helps to soften their skin and makes it easier for them to shed.
Any sand substraight, even calci-sand, can cause impaction if they eat too much of it. But if your gecko is still active it doesn't really sound like impaction - plus I'm not sure he'd live 4 months with an impaction.
I'm not sure of any reptile vets in that area, but until you find one fixing his temperatures is going to be a good start. Is he still active and moving around and all that?
Good luck! 4 months is a long time for him to go without eating but hopefully he'll eat for you soon!
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