Smart Prepaid

For context, I availed what supposedly a 3 month load plan sa Smart for 699 each month. Due to lack of time since I’m a full time working student, di ko na cancel so I paid for it for 5 more months. I was behind for just a month and the services (data plan) is no longer working. Nagpakampante ako kala ko ma c cancel na since di ko na nagagamit services nila. Until I’ve been receiving messages from smart that I owe 3k! It is legal for them to charge me for the months I haven’t use their services? Bayaran ko na lang po ba and cancel it sa office nila mismo sa mall? Help your 20 year old girlie out🥺🙈