The one I used when I lived in Dr was PO Box International . I never had a problem with them. I will be using them again when I return. They have the Miami address and then bring the mail to DR. You have to pay the postage from USA to DR when you pick up your mail.
These are some of the other mail services I know of. EPS, CPS Continental, Mail Boxes Etc.
I can recommend Business Mail if you live in POP, Santiago or Santo Domingo. They have prices that are a little better than the competition, and use the same system, ie., you mail goes to a drop in Miami and they bring it down here.