Guarantee on drilling projects

What is the general laws concerning guarantee on drilling projects in Nigeria?  In August we sponsored a borehole for a local community in Nigeria.  The contractor drilling the borehole was the same guy whom had committed a geo survey beforehand.  Now, half a year after the inauguration of the water service the borehole has collapsed with the pump inside.  Allegedly he casing that has been used has been to weak.  The contractor offers a discount on a new borehole, but I'd say he should take full responsibility and cover the new borehole and pump entirely.  Has anyone been in a similar situation? What did you do?  Does someone know if there are laws that'll back our claim? Best regards Charlie