How to avoid Database Lock using Entityframework Transaction

Question

I have a method where I save several classes and call another method to do an optimization on top of these classes, but I am using Transaction, in case something goes wrong in this optimization I need to give rollback.

Transaction

using (var context = new AppContext())
{
    using (var dbContextTransaction = context.Database.BeginTransaction())
    {

I tried to change the isolationLevel so:

using (var dbContextTransaction = 
                 context.Database.BeginTransaction(IisolationLevel.snapshot))

Yet he still gives lock at the bank, I wonder why this happens and how I would get around this situation, basically I would like to do a Optimistic concurrency control, without checking at commit time, simply the last version is saved.

Obs. using some commands directly in the database I get the experienced behavior, but it seems to me that the isolationLevel that I Seto in Begintransaction is not serving at all, in case someone can explain to me the functioning and clarify me what I am missing, I will be grateful.

Commands used:

ALTER DATABASE [DB] SET SINGLE_USER WITH ROLLBACK IMMEDIATE
ALTER DATABASE [DB] SET READ_COMMITTED_SNAPSHOT ON;
ALTER DATABASE [DB] SET ALLOW_SNAPSHOT_ISOLATION ON;
ALTER DATABASE [DB] SET MULTI_USER