If/elseif statement within wp_mail function

This is problem with your PHP syntax, not WP. You are using assignment (=) where you should be using comparison (==).

So this:

if( $problem_type="phones" )

should really be this:

if( 'phones' == $problem_type )

And same for other condition.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)