I would advise you to contact the care home and say you would like an appointment with the manager and the care staff who usually look after your mum in the evenings and at night.
Point out, that while you know she is in a care home, not a brothel, and that presumably no-one is trying to creep into her bed (although I did once experience an old woman who maintained she was in her bed, when she actually was insisting upon getting into an old gentleman's, always the same man's and only if he was in his bed. The s taff attributed this to her dementia.) it is distressing for you to have to try to calm your mum down over the phone long after your bedtime, and that some other way of calming her needs to be found.
They are after all trained to deal with this sort of thing, you presumably are not, and have placed your mother in a care home because you know this is necessary and best for her.
Try to get them to agree with you on how THEY tackle this, and ask them to inform you the following day after nine a.m. if there has been another incident of this kind. There is no point in both you and your mother being unable to sleep after all.