You may absolutely sue the builder for these bills, on one of two likely grounds:1) breach of contract--these were additional costs not in the contract of sale and therefore for which  you should be liable; you contracted to buy a house a) for a certain total price and b) free and  clear of anything that could potentially affect title (e.g. liens could have been obtained for these bills)2) fraud--they builder misrepresented to you by not disclosing the existence of unpaid bills; since it's material, or important, to know whether or not your buying a home that has liabilities already attached to it and which could have trouble with utilities, these were things that should have been disclosed