Hello @lizazim and welcome to Yhteisö! I hope you will find our threads and articles useful! 

A prepaid subscription is valid for 6 months from activation or 12 months from the last top-up, after which it will be closed. And once closed, it cannot be reactivated. Here’s more information about Telia Prepaid. 

A quote from Telia Prepaid instruction booklet:

Period of validity

You can activate your prepaid card until the date indicated on the package. After this, activating the prepaid is no longer possible.

After activating the prepaid, it will be valid for six (6) months. Each top-up via the balance or a package extends the prepaid’s validity by 12 months.

Only topping up effects the validity. Having your phone turned on or off has no effect on the validity period.

Thanks for the answers!