Fatal error while upgrading presta shop

[Czolg]

Hello,

i tried to upgrade my presta shop from version 1.6.1.9 to 1.7.6.2 and had plenty problems with it, resulting now in not being able to log into prestashop panel and the web site is down. I tried to use 1-click upgrade. As i tried first problem with back up occured. So i made back up manually and switch off back up option in 1-click upgrade module. Still didnt work so i updated PHP on my server from 5.6 to 7.1 and tried again. Everything was going good until fatal error occured. So i copied back all the files i backed up and now the website is still not working... the error that comes out right now is

Fatal error: Uncaught Error: Call to undefined function ContainerBuilder() in /sklep/config/bootstrap.php:34 Stack trace: #0 /sklep/config/config.inc.php(57): require_once() #1 /sklep/adm40271/index.php(36): require('/sklep/config/c...') #2 {main} thrown in /sklep/config/bootstrap.php on line 34

bootstrap line 34 $container_builder = ContainerBuilder();

Please help