My unpaid iPhone 7plus

If you bought it through Apple then you can reach out to Apple Support directly. Depending on your region, you may be able to reach them here: contact Apple Support 

If you bought it through a network provider then call their call centre.

If your dad is paying then he will have to call them.

Look at the contract you had with whomever they are.

We, just users like you, cannot be aware of your transactions with Apple or with the store where you bought that device from.

Regards

Giulio