unyielding

Not giving way to pressure; hard or inflexible.

Incapable of being changed; unalterable.

Not willing to change or be persuaded; resolute.

Not yielding to force, persuasion, or treatment; unbending; unpliant; stiff; firm; obstinate.

Not giving in; not bending; stubborn.

resistant to physical force or pressure

stubbornly unyielding