Does anyone know the best way to retrieve a broken drill string from a deep well?

We are constructing a community borehole in Abia State Nigeria - trying to dig a 400 feet deep well (125 m). We have had a bad incident occurred twice using the HF-3 Chinese Rig. The drill pipe broke down at about 200 feet two times. Our first conclusion is that the drill pipes are sub-standard (less than 6 mm wall thickness - though manufacturer claims that it is 6 mm, but we think the pipes that have welded thread ends are of poor quality and bad material used in the manufacturing. Also does not look like what  was shipped to us was exactly what we ordered). We plan to revert to using an older Schramm T-64 rig with 4.5" drill stems in the region as soon as we have funds to continue the project to completion. Meanwhile, does anyone know how we can retrieve a broken drill string from a faulty tool joint? The well depth is 215 feet and the break is at about 65 feet from ground. The soil formation is mixed of sandstone / shale and the diameter of the well is about 10 inches (was using a 9 inch PDC bit to ream down when it happen.) Well diameter also appear to be wider than 10 inches in the area of the break.  Our team has been unable to grab the head of this drill string. The pipe diameter is 2-3/8 inch and pipe lengths about 3.2 meters (11.5 feet) each. A. Sunny Okorie  (Country Director, RNM in Nigeria) Contacts:;; +1-832-385-3229; fax: 866-587-2032