For active subscription, you can install Ps from CC app up to two systems irrespective of OS (can be both Win/Mac or one each).
but if a Retail CS6 Serial Number then you can install on two systems same platform(Win or Mac). This depends for which platform you bought the SN for.
But if you still need any help in deactivating please contact Activation Support:
Click the Chat Now button at the end of the page and talk with a live agent who would resolve it ASAP.
Hope this answers your query.