Kids suffering due to a family argument?

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A family argument occured in August 2010 on my partners side and my kids are suffering from this. His mum has shut off contact with us completley and is not interested in speaking to her grandchildren. Alot has happened to my oldest daughter since this like going on holiday, getting glasses for the first time and starting nursery and not once has she bothered to pick up the phone to speak to her and ask how everthing has gone. I spoke to his mum a few weeks ago and told her i felt like she was not bothered about my children and her reply was "Why should I be" which really dusgusted me. I have not told her she can't see them but in order to see them she would expect me to take them backwards and forwards to her house rather than her making any effort. I really need advice as my oldest daughter is starting to ask questions as to why she hasn't seen her nannan in a while, please help! Thanks