Son and son's wife keeps telling me I am not a good grandmother, they live 12 hours away from me. ?

we put a limit on Christmas last year for the kids, we set a 400 dollar limit, DIL asked that we spend it all on a gift for our son. We agreed but told her that would be it, she agreed, and stated that the girls ( 2yr old twins) would not know the difference that they would receive lots of gifts from other relatives. We agreed with the gift (safety item for motocross racing) since she told us that the best gift we could give the girls was to make sure there daddy was safe. Come Christmas day all hell broke loose and our son was ticked because we did not send any gifts for the girls. We explained what we were told to do, he still was mad. I later heard from mutual friend that my DIL was telling people that we bought the girls nothing for Christmas. I was hurt and called my son to ask him to please tell DIL not to do that and if she was to tell anything to tell the whole story. The next day DIL called screaming at me and telling me that I was going to loose my son and that I was a horrible grandmother. We told our son what she had done and he more or less condoned her behavior. DIL will not take my calls or talk to either of us now for over a year.. We have been in communication with son, but it is estranged. I still send the girls gifts for almost every holiday, have talked to them on the phone, but was told by son just recently that I am not a very good grandmother. I told him it is hard to have relationship knowing the feelings of his wife, he informed me that when we were more in contact with his children and acted like better grandparents maybe she would come around and have something to do with us. He accuses me of never of liking his wife, I told him I love her I just don't appreciate her way of confronting me. They have lived 12 hours away for almost 4 years now, I have been out there 4 times have called and done video cams with them, sent the girls tons of gifts and it seems its never enough for him or her. I told my son that his father and I for some reason cannot do right by him, he said nothing. He complained alot abut his father and said some pretty mean things about him, but when I talked about his wife and how she needs to not confront me in that matter he becomes irate and hateful. What do we do. I could go on and on about this. Our true feelings is that she wants our son all to her self and I am fine with that, he is suppose to leave his mother and father and cleave to his wife, but she is truly the one who dislikes me and his father, she is very controlling and hateful. I have apologized several times about not sending a gift for the girls and I was wrong but I was blown away when my son just told me recently that they are upset because we don't make enough effort towards his girls, that it has nothing to do with the gift. I want this to be better, have tried to work it out, but they are making conditions, and she always has rules and hoops that me and sons father must jump through.