If the software works on the machine then it must have been licensed by whoever installed it or else it would not still be working. IF the license is held by the company you say no longer works with your company then chances are they own the license and your company will have to purchase their own copy. Howbever, CS5 is not currectly sold by Adobe so your company would have to consider the current options... CS6 or a Creative Cloud subscription.
You should talk to Adobe Support directly if you have not already done so.
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