I bought a subscription for 3 devices through retail. This worked on 2 devices but will not install on the 3rd. Uninstalled all reference to nortons but it keeps reactivating the old version and norton claims all 3 were activated.

I bought a subscription for 3 devices through retail to replace an expiring subscription. This worked on 2 devices but will not install on the 3rd. I Uninstalled all reference to Nortons from the device to see if offered a fix but downloading the new version does not work, it keeps reactivating the old version. An additional issue is Norton claims all 3 were activated. 

First would be having Norton recognise that protection was installed on only 2 of the 3 devices paid for. Some part of Norton does acknowledge this as Norton sent a email informing I had not used all the protection paid for. I used the download file from that email to attempt to activate Norton on the 3rd device but it reactivated the old version..

I followed an earlier forum advice about opening Norton, activating help then inputting the product key. This did not work because Norton responded that there were no more devices to be activated against that product key, i.e 3 had been used. 

Any ideas please?