Issues regarding website with old code

Hello all,

I'm currently maintaining a website for someone. The site worked most of the time correctly, but since the webhost upgraded to PHP 7, the website does not work anymore.

I discovered the website is using CI 2.0.2. I got the same errors in debugging as:

https://stackoverflow.com/questions/4384...p-to-php-7

And solved them all. But still the page keeps blank. When I go into the log files I get this:

[Sat Jan 04 23:38:57.942225 2020] [fcgid:warn] [pid 4267] [client xxx] mod_fcgid: stderr: PHP Fatal error:  Uncaught Error: Call to undefined method CI_DB_mysql_driver::initialize() in /home/xxx/domains/xxx.nl/public_html/system/database/DB.php:146
[Sat Jan 04 23:38:57.942250 2020] [fcgid:warn] [pid 4267] [client xx] mod_fcgid: stderr: Stack trace:
[Sat Jan 04 23:38:57.942255 2020] [fcgid:warn] [pid 4267] [client xx] mod_fcgid: stderr: #0 /home/xxx/domains/xxx.nl/public_html/application/third_party/MX/Loader.php(94): DB(Array, NULL)
[Sat Jan 04 23:38:57.942260 2020] [fcgid:warn] [pid 4267] [clientxx] mod_fcgid: stderr: #1 /home/xxx/domains/xxx.nl/public_html/system/core/Loader.php(1024): MX_Loader->database()
[Sat Jan 04 23:38:57.942264 2020] [fcgid:warn] [pid 4267] [clientxx] mod_fcgid: stderr: #2 /home/xxx/domains/xxx.nl/public_html/system/core/Controller.php(53): CI_Loader->_ci_autoloader()
[Sat Jan 04 23:38:57.942269 2020] [fcgid:warn] [pid 4267] [client xxx] mod_fcgid: stderr: #3 /home/xxx/domains/xxx.nl/public_html/application/core/Public_Controller.php(13): CI_Controller->__construct()
[Sat Jan 04 23:38:57.942274 2020] [fcgid:warn] [pid 4267] [client xx] mod_fcgid: stderr: #4 /home/xxx/domains/xxx.nl/public_html/application/modules/producten/controllers/producten.php(9): Public_Controller->__construct()
[Sat Jan 04 23:38:57.942278 2020] [fcgid:warn] [pid 4267] [client xx] mod_fcgid: stderr: #5 /home/xx/domains/xxx.nl/public_html/system/core/CodeIgniter.php(288): Producten->__construct()
[Sat Jan 04 23:38:57.942283 2020] [fcgid:warn] [pid 4267] [client xxx] mod_fcgid: stderr: #6 /home/xxx/domains/xxx.nl/public_html/index.php(200): require_once('/home/xxx/d...')
[Sat Jan 04 23:38:57.942287 2020] [fcgid:warn] [pid 4267] [client xx] mod_fcgid: stderr: #7 {mai in /home/xx/domains/xxx.nl/public_html/system/database/DB.php on line 146


I'm not that expert on debugging and not familiair with C.I. How can I resolve the issue?

When i disabled the initialize () calls (as I added __construct()) I get:

[Sat Jan 04 23:54:36.612571 2020] [fcgid:warn] [pid 2450] [clientxx] mod_fcgid: stderr: PHP Fatal error:  Uncaught Error: Call to undefined function mysql_query() in /home/xx/domains/xxx.nl/public_html/system/database/drivers/mysql/mysql_driver.php:163

Is there a config setting to switch to mysqli? Or do I need to do something else?