How to filter timestamp column in Data Flow of Azure Data Factory

I have timestamp column where I have written following expression to filter the column:

contact_date  >= toTimestamp('2020-01-01') && 
contact_date  <= toTimestamp('2020-12-31')

It doesn't complain about syntax but after run it doesn't filter based on date specified. Simply to say logic doesn't work. Any idea?

Date Column in Dataset:

Solution

Please don't use toTimestamp() function. I tested and you will get null output.

I use a Filter active to filter the data. Please use the toString() and change the expression like bellow:

toString({contact_date })>= toString('2020-01-01') && toString({contact_date })<= toString('2020-12-31')

Ref my example, contact_date and output: