Working for a call center that is run by the bank should be avoided. Although the person isn’t directly involved in riba, his action is supporting these banks. Furthermore, his salary in this scenario isn’t completely haraam but he would be in sin for cooperating upon transgression.
And here is a fatwa of Ash-Shaykh Saalih AaliShaykh concerning the matter:
AbdulFattaah Bin Uthman