Repairing product filter in Opencart

Hello,

we have Opencart webshop all set up and in production. We have some minor issues with page. We have working filter for categories. There are some issues with our filter.

1. Index page – not all car brands are listed under the left “brand” filter, for example Peugeot.

2. Category issues – if you select any item from the category nav bar, for example “control unit” and filter by car brand name, Peugeot, once you select the second page, it lists all control units, not just Peugeot.
With other words:
If you go to for example
https://dev2.rabljeni-avtodeli-jung.si/en/electrics/control-unit
and filter Peugeot
https://dev2.rabljeni-avtodeli-jung.si/electrics/control-unit&C=EUR&filter=Brand_a-n-18=Peugeot
then 2nd page is not working:
https://dev2.rabljeni-avtodeli-jung.si/electrics/control-unit?page=2&filter=&filter=Brand_a-n-18=Peugeot&C=EUR

Site:
https://dev2.rabljeni-avtodeli-jung.si

there is .htaccess protection;
us: modular
pass: piecesMakeHol333

Please estimate in how many ours you can solve issue. If you need any additiona information please chat me and I will answer.