Money with held for no reason in my savings account.

I have R400 blocked on my savings account for past 4 years since 2016. Apparently I took out a smart device but I never ever had one. I can't draw or transfer my R400. I call fnb numerous times and transferred up and down all departments. No one can assist. Also the phone got dropped on me about twice. Pathetic service. I'm going to change banks soon.