Social services are making false allegations against me to my partner calling me a child abuser with no evidence. Have I got a case?

My partner received a phone call from social services claiming that they have evidence that i am a child abuser and molest children. My step daughter has had to go and live with her grand parents as they threatened to take her away otherwise. We've had no letters and they haven't had the decency to ring and notify me of their allegation. My partner surfers from anxiety and she has been in bits from these allegations and has been worried sick. My step daughter is confused why she cant come home and why she cant see me. I am an open book and nothing to hide. I need legal advice as I am prepared to take legal action against them. I need help please .