About 80 people attended a public meeting about Owen Mor nursing home on Thursday evening.
The home, on the Culmore Road, remains closed to new admissions after the health regulator, the RQIA, obtained a court order over health standards concerns.
The nursing home first came under the spotlight in May following an inspection.
Ciara Stewart said her 76-year-old father-in-law – who has a form of dementia and has lived at the care home since March 2018 – had not received the basic care he needed.
“We only realised when we spoke out that we weren’t the only family being affected,” Ms Stewart said.
“Hopefully we can make a fundamental change moving forward.
“Competent care was the main issue for us.
“It was in relation to basic nursing.
“We thought the staff would have the competencies to direct us. Lewy body dementia was new to us and we thought the guidance would be there for us.
“That’s not what we got.”
Ms Stewart said her family’s experience had been “horrendous”.
The 81-bed facility is for people with learning difficulties, mental health issues and dementia.
In May, inspectors highlighted concerns about staff knowledge, including nurses not following policies and procedures.
They also found inadequate records about areas of patient safety, such as falls, feeding and nutrition.
After a follow up inspection in August, the regulator formally stopped new patient admissions after obtaining a court order – an unprecedented move, according to the RQIA.
A spokesperson for Owen Mor Nursing Home said: “The staff and management are working closely with the RQIA and the Western Trust to address four outstanding compliance issues.
“We regret the unavoidable delays in achieving full compliance and any knock on effect this has had due to the suspension of new admissions.
“We have reassured our existing residents and their families that they are receiving a high standard of care and this is constantly under review by RQIA and the Western Health and Social Care Trust.
“We wish to address allegations made by an individual resident’s family and while it would be inappropriate for us to identify any individual, we welcome them to engage with us directly via our complaint’s procedure. Complaints will be robustly and rigorously investigated through the appropriate channels.”
The RQIA confirmed that Owen Mor remained under enforcement action, and it was “continuing to monitor the nursing home to ensure its managements make the necessary improvements to address our concerns”.
The Western Trust said it had been working closely with RQIA and Owen Mor to address concerns identified by the RQIA.
The trust said it was having regular meetings with Owen Mor’s management.