Written with people moving from Turkey in mind. The Portuguese rules still apply more broadly.
Canceling Internet When Leaving
Breaking a 24-month internet contract usually incurs a fine. However, "Emigration" is considered a valid reason for penalty-free cancellation. You must provide proof, such as a deregistration certificate from the municipality or a work contract abroad.
Simply moving to a new house within Portugal is not a valid reason to cancel unless the provider cannot supply service at the new address. Always submit your cancellation request in writing.