If it's registered & insured & if it got here, it should be sitting in your local Post Office in DR. They won't deliver because they need your signature.Take your ID with you - cedula if you have it, passport if you don't have a cedula. A friend in US sent 2 packages to himself, addressed to a hotel in Sosua - never got delivered but he tracked it to Puerto Plata Post Office & was able to collect from there.
We've had a P.O. Box in PP for 14 years - only used for non-valuables, Christmas cards etc. About 8/9 years ago the system used to work really well (& most of our mail came from UK) but over the last 5 years the system (for want of a better word) has deteriorated.
jupe, here is INPOSDOM's website with 2 email addresses if you want to email them:
Bienvenido a INPOSDOM