can not access service menu with either key combinations

[erdem_ua]

Service menu disabled on postFeb 2010 firmwares. So I believe you have such firmwares. So you can't enable boot menu..
Also you make bad thing by discarding warnings about bootloop. You needed to put your mount/bind into safe region at bellow, not as a first line at SamyGO.sh. So you cannot recover your TV from bootloop via USB attaching...

Notice that, if you upgrade postFeb 2010 firmwares and reverting back will erase your uboot partition and also your linux image will be changed and that result you cannot use exlink port at all... This will also deny access from ExLink port. I think it's better to call service.

[erdem_ua]

Yes but I don't recommend it to patch latest firmwares because they are really really restricted... Instead, you needed to use FFB (flash firmware back) than use old version-ed and hacked firmwares is better for your enjoyment.

[erdem_ua]

You don't needed to change script. Just let it make its job. You can say NO to changes other than advanced mode...
Also "DO NOT" use latest firmwares. They are not SUPPORTED nor SAFE such a thing on them. It **might** be work with it but no one tested. So you can easily brick your TV, without recovery...
You have better to use FFB to revert older version.