How can I prevent coconut cream from curdling in a soda drink?
If it's acidity that's causing the separation, a pinch of baking soda should do it. In fact (trivia alert!), the first "soda" was naturally carbonated spring water, which usually contained alkaline sodium compounds, including sodium bicarbonate, a.k.a. baking soda. Many brands of carbonated water today, especially those marketed as "club soda" in the US or "soda water" in the UK, have baking soda added to mimic the flavor of that natural spring water.

Having said that, if coconut cream curdles with acid, and you've already added lime juice to your coconut cream, there's nothing you can do to un-curdle it. However, coconut cream has very little protein, which is what causes dairy milk to curdle in acid. Most of the discussion I can find online about coconut milk and cream curdling refers to heat as the main cause.

Could your problem simply be that the high-fat coconut milk, like many fatty products, doesn't mix easily with water? Try blending it thoroughly with a small amount of water, and then blend that with the larger amount of carbonated water, and see what happens.