A single Android account would be purchased through Coogle play and not through Piriform/CCleaner.
That means that your subscription for it is with Google not Piriform/CCleaner.
If you want to cancel that subscription then you will need to cancel it with Google Play:
Once the Google subscription has been deactivated you can then re-register CCleaner Android using the multi-device key that you have now got for Pro Plus.
That involves upgrading the Free version using the ‘I have a code’ option - the code being your Pro Plus key.
The support server has been down for a number of days, but when it comes back up here is a guide to registering/activating CCleaner Android with a Pro Plus or Premium licence Key: