why is it happening? when you're blocked, all data indicators like 2G/3G/4G are blocked/disabled and now since you're using LTE upgrade sim which upgrade you data connection to 4G, it will bypass the block/disabled indicator in their system and thus 4G is unblocked except for 2G and 3G.
Now, if you want to bring back the 2G and 3G connection, you should call their hotline to fix it for you.