Sorry to hear that, about your experience with our Samsung Service Center and it's staff behavior towards you and we really apologize for the inconvenience it caused you.
If it happens to me, I will feel the same, given that we expect every one to treat you with utmost care and respect while conducting business.
I agree with you, that our Tech support should advise you beforehand that in order to protect your data and your privacy, your device will go through a back-up process and factory data reset.
Once again, accept our sincerest apology and rest assured that we are treating this as a serious matter and further coordinating with the dedicated team/department in order to take appropriate action.
For more assistance and guidance, you may contact us on our online Samsung Customer Care support channels below.