Additional field in customer profile

[prt_shopping]

I inserted a new field "Additional VAT" in Profile, during registration proccess the field is instereted in Database, table "ps_address", i want do get the value also in customer profile in backend, see image.

 

 

The code to get firstname from db is in AdminCustomers.php, and this 'firstname' is also in db the same: 

htmlentities($this->getFieldValue($obj, 'firstname')

my code with true row name is:

htmlentities($this->getFieldValue($obj, 'addvatcustom')

but i get a empty value, the field in db is filled.

 

How can i get here the true value and also true update functionality?