How to recover funds owed when business change their name ?

You write that this business has changed its name.  If that is all that is going on, the same entity has changed its name, that would not affect your right to the funds due you, and you could start a lawsuit to recover.  However, it may be a new legal entity.  In general, the owners of corporations (shareholders) or other legal entities are not personally liable for the entity's debts, and neither is the purchaser of an entity's assets.  This is probably the primary reason why people incorporate their businesses, and why, if they sell them, they sell the business's assets (equipment, customer list, lease, etc.) rather than its stock.  If this new business is a new entity which has purchased the assets of the old, it would most likely not be liable for the old corporation's obligations.  There are exceptions, but they are rare, and you haven't provided enough information to determine what exceptions might apply.