How can we get our unrightfully retaied deposit back

In short; landlady holds deposit unrightfully while claiming to have proof. Proof requested, now we get ignored. Gave her 2 deadline, ample of time. Where can we turn now? We are not in Spain. We do have N.I.E. The rent was a regular tenancy, not holiday even though it was only for 6 weeks and meant for holiday.