If your unli data has expired and you have tried to register for it again but received a message saying "you can only subscribe to this offer once," it means that the specific offer you are trying to avail is a one-time subscription only.
In this case, you will have to look for another offer or data promo that is available for multiple subscriptions. TNT (Talk 'N Text) typically offers a variety of data promos with different durations and data allocations. You can check their website, social media pages, or contact their customer service to inquire about the available offers that you can subscribe to multiple times.
Alternatively, you can consider other telco providers that may offer data promos that allow multiple subscriptions. It's always a good idea to compare different options from various providers to find the best data promo that suits your needs.