PLDT annoying interrogation after filed application has been approved.

Dear Sir/Madam, my sister had a balanced to this company but before that she called up the company for disconnection request many times because the Internet connection was not good and PLDT always assure that they will respond to my sisters request but still they send bills, then sister called again to request again for the disconnection and still another bills until they sent my sisters notice of disconnections if bills are not going to settle. After a few months my sister wanted again to apply for the Internet connection to the same company but sinced she doesn't want to pay for the bills that she certainly never used and they sent a notice again that my sister an the address was already blacklisted, but sister really want to apply again and so she asked my brother in-law for help to pretend as a new tenants on the same address so my brother in-law applied for the pldt landline and Internet connection then they approved it. After a few days there's a call from the PLDT company that seems to be interrogating, asking if we have internetshop and if sister still lives in the house and the PLDT call center agent even ask if I am my sister and she also ask if I'm connected from the person who applied for the connection. I am annoyed for this situation I was thinking that why would they interrogate us the application was already approved. I am concern for the customer's right. Can you help us or any advice what will be the right thing to do. Thank you so much and more power. God bless:-)