Husband has no respect for my mum

My husband has no respect whatsoever for my mum. I married an older man Who is 10 years younger (typo) than my mum. My mum wants to be called mum by my husband but my husband has simply refused to do this. My husband will walk into a room, see my mum there and not even acknowledge her by greeting her. So many other instances where my husband has no regards for my mum because they are close in age. I don’t know what to do. My mum has stopped visiting as much as she used to do you to this and now she feels by the way that my husband treats her.