Having been in your shoes I know exactly what you are going through, As grandparents we took our sons girlfriend (they are not married) to court to gain access, the court awarded us access on set days, It creates further problems and being as stroppy as she was she was generally causing more problems (not having them ready on time) things like that, it really didn't work, the strain got worse and in the end we let it drop and let her do things her way, the children miss us we know that, she is punishing them in a way that imo the children could resent her for this later in not giving them more time with us. The advice on social services is correct, you have a duty to contact them if you fear they are being neglected, I didn't do that because the children when I saw them were always well dressed and fed, they were fine, my son stands with her on this and this created strains on our relationship with him, it had a tremendous toll on my wife (his mother) in the end I told them that they were not helping the situation, we were told often that we would never see them again, she had not forgot that we had taken her to court so that festered with her really.She looks after the children well, so I couldn't go any further tbh, your situation seems different in that you seem to have legitimate concerns, you also seem to be at her beck and call with altered/changed arrangements, that was another thing we clashed over, I thought that was very unfair then to get a call saying thanks but i'm here now is not fair on you either. I hope it works out for you, there is no easy answer as thousands like us will testify to!!