There are 2 banks in Los Gigantes. Santander and Caja Canarias
In Playa Arena there is Caja Canarias, La Caixa (Banco Pastor closed and merged with the Los cristianos branch)
The Puerto Santiago still open is BBVA, but Caja Rural has moved to Alcala.
In Alcala there is Santander, Caja Canarias, Caja Siete and Caja Rural
(If the above information is not correct please send me a private message and I will modify the above info)