Grandparents seeking time with grandchildren

We recently looked after put gc for several weeks due to our dd having problems with her mental health & narcotics. They are 2 & 4 years. We have had them to stay every weekend since babies & felt we had to step in for them when dd was struggling.
My dd saw her dc 3 times over 6 weeks when they were staying with us. Social worker got involved a few weeks after the gc had been here but my dd took the children back unexpectedly on the 4th visit.
She then stopped me & my dh from seeing our gc at all. We were devastated but thought she'd come round.
She has now agreed with the social worker that we can see them one hour a week, gc are very confused & I've explained our worries to the social worker. This hour is very controlled with my dd saying it has to be with my dm - who gets a certain time to get them to us & get them back. Poor kids are stressed out, my dm who is quite elderly finds it stressful too. If they're late my dd is on the phone asking where they are. We've written to the SW but apparently she's now been told by my dd not to have any contact with us so we are being pushed out of our dgc lives. We have also tried to persuade our dd to let her dc stay longer ( the eldest asked her outright according to my dm). My dd will only allow this one hour a week.
Has anyone else been in this position?
My dd has done this before when the youngest gc was a baby & it went on for months.
We are thinking about court action but not sure what time we would get with the gc. Does anyone have direct experience of family court as grandparents?