Credit Rating Issue

I have good credit and the mobile device customer service stated that I cannot even qualify to upgrade my paid off device with a new one. I no longer qualify to use the payment plan deal. 

I have 5 lines and had payments plans on 4 devices at once. Now three have been paid in full. This is not accurate and the customer service had no answer other than to use another SSN! I would prefer to use my own, that would be the legal choice. He corrected to say I could have a family member add credit to my account that way. That is absurd when I am the one that co-signs for others. 

How can my credit rating be corrected with Xfinity? The customer service told me to change my credit rating at the “government office.” He clearly doesn’t understand where a credit rating comes from! 

please help