Symfony 2.8 Upgrading Packages Problem For PHP 7.0 - php

Question

Yesterday I updated my PHP version from 5.6 to 7.0 in a docker project using Symfony v2.8.51 where I'm now facing the issue of some of the dependencies not working.
I upgraded my packages but I am getting an error for the doctrine bundle package.
When I load the project in my browser I am getting:
Unable to load class "Doctrine\Bundle\DoctrineBundle\Registry"
in ClassCollectionLoader.php line 309
at ClassCollectionLoader::getOrderedClasses(array('Doctrine\Bundle\DoctrineBundle\Registry', 'Doctrine\Common\Annotations\DocLexer', ...
the function this error is referring to looks like this:
{
$classes = array();
foreach ($class->getInterfaces() as $interface) {
$classes = array_merge($classes, self::getInterfaces($interface));
}
if ($class->isUserDefined() && $class->isInterface() && !isset(self::$seen[$class->getName()])) {
self::$seen[$class->getName()] = true;
$classes[] = $class;
}
return $classes;
}
My composer json requirements look like this:
"php": ">=7.0",
"symfony/symfony": "^2.6.4",
"doctrine/orm": "^2.5.0",
"twig/extensions": "~1.0",
"symfony/assetic-bundle": "#stable",
"symfony/swiftmailer-bundle": "#stable",
"symfony/monolog-bundle": "3.0",
"sensio/distribution-bundle": "~2.3",
"sensio/framework-extra-bundle": "~3.0",
"sensio/generator-bundle": "~2.3",
"incenteev/composer-parameter-handler": "~2.0",
"friendsofsymfony/jsrouting-bundle": "2.0.0",
"jms/serializer-bundle": "#stable",
"liuggio/excelbundle": "~2.0",
"ircmaxell/password-compat": "~1.0.3",
"stof/doctrine-extensions-bundle": "~1.1#dev",
"symfony/console": "^2.5.6",
"imagine/imagine": "#stable",
"liip/imagine-bundle": "#stable",
"soundasleep/html2text": "^0.5.0",
"snc/redis-bundle": "1.1.10",
"predis/predis": "^1.0",
"stackify/monolog": "~1.0",
"lexik/maintenance-bundle": "^2.1"
},
I’m not sure what exactly I need to do to get it to work again or what would be the best approach to upgrade all of my dependencies correctly since I don't have a lot of experience with it.