Hi Dudoos and welcome to the forum. On the assumption that you are also new to the site, this FAQ should help you find your way around.
Welcome to Benefits and Work
A quick search reveals that TNS BMRB are a bona fide research company who work for, but are not a part of, DWP. You have every right to not answer their questions if you so wish. All I can suggest is that you ask them to remove your details from their database. If the calls still continue maybe you could get some help from your MP
Contacting your MP