such a sad situation for you to be in,not just grieveing but being cut off like that - although of course his mum must be in a bad way as well - it is difficult to know what to advise, did you get on with her before ? - -
I lost a partner to cancer years ago and even though i certainly wasnt cut off the way you have been there are some elements i can relate too. I was Marks primary carer during his illness, he lived with me i spent weeks at hospitals with him etc etc - and in the end found myself being the one having to tell his parents that he wouldnt recover - afterwards i wondered whether in some way it was that which in the end turned them against me - had i said or done something the wrong way, could i have worded it better - but i and they were there when he passed away.
Afterwards they made their own way home - no offer of a lift and i had to ring a friend to collect me. I didnt hear from them again until the funeral was arranged, because as we were not legally married they were next of kin and i had no say. I saw the notice before they rang to say when it was.
I went to the funeral and it wasnt what i, or he would have chosen to do but it wasnt for me to say.
I went to the funeral tea and wasnt introduced to other relatives or sitting at the main table and ended up leaving very early with a couple of his mates who didnt like how i was being treated.
I didnt hear from them again until they arrived to collect his car and guitar which was part of his estate. - so even though i knew what happened and had some communication with them i felt very sidelined and confused. A couple of years later i heard his mum had been praising the way i cared for him during his illness and not long afterwards i saw her - and she said she hadnt meant to do it, she felt awful about it now, but at the time, she couldnt deal with my grief on top of her own - and i really believe she meant that and it was genuinely the reason she cut me out.
But its different for you, you have too many unanswered questions and didnt get any communication about the funeral.I wonder if you could try writing too her - an old fashioned letter - tell her you cant begin to imagine just how devastated she must be to lose her son but gently point out that you miss him too, his smile and his personality and credit her parenting with some of that, just to try and get her to talk about him as he was, do you have some recent photos you you could make prints of for her - perhaps suggest that she might like to have a copy - (dont just send them in that first letter ask first) perhaps then she might have to communicate if she does want them.
Looking at the date this happened and given the circumstances, it is possible that there may have had to be an inquest so the cause is not yet official - aternatively you may be able to see a copy of a death certificate.The death would have been registered locally to where it happened i think.
Aside from their reaction and the questions you need answered I would give some serious thought to creating your own memorial, which will help focus your grief on what the two of you had not on other aspects of his life and the anger and sadness you must be feeling in being on your own with his.
There are a few ways you could do this - from looking into planting a tree in a memorial woodland to something personal just to you - i planted native daffodil bulbs in the places we loved most when i lost my husband (not Mark, a more recent loss) - doing it forced me into some kind of action,just the planning helped me think beyond the bubble of pain i was in,and now i can return too those places every spring and see them come up. I also decided i would live my life for him - do the things we loved doing do the things we said we would but never got round too for him, - so in a way he is always with me and he is always pushing me on to do more.
