Hi @webbc, thanks for your post here in the community.
As @Ernie_C has mentioned, if the Netflix bundle wasn't incorporated or available at the point you took out the contract within your package, then yes you would need to take out a new 18 month contract for the relevant package where it's included.
I appreciate you may have already made your decision based on this information, but I hope this helps and please let me know if you need any more advice.
Many thanks
Tom_W