I see Caribe Tour goes up to Jabacoa, I guess you go from Sosua to La Vega and then change bus there to Jarabacoa.
After that from Jarabacoa to Constanza you must find other transport. But I am sure there must be more options from La Vega that takes you direct to Constanza, may be a gua gua of some sort..... !?
Here is Caribe Tour website, you can see the routes and prices there:
Caribe Tours | Portada