Parents not speaking to me!

I had my son when I was 31, my only child so far, after the birth of my son I asked my parents not to smoke in their house while he is there, and they said sure no problem. When my son was 3 and a half my husband and I descided to move to a different province to make more money and better ourselves and that's what we did, this past January we went back home for a visit 5 days total, we had so many friends we wanted to see, even if it was a short visit, the first day we arrived we went to my parents house for a few hours to visit in the morning and my Mom asked me if we wanted to go for dinner the next day (Saturday) my Mom does not work and my Dad had a few weeks off, I asked her if we could make it Sunday or Monday because good friends of ours were off for the weekend and had planned an ice fishing outing, my Mom said OK sure, Sunday and Monday went by and they never invited us for dinner again the whole 5 days we were there, we went to visit quite a few times, the 2nd time we went to visit they had been smoking in their bathroom while we were there, seen smokes ashtray and lighters in the washroom, the plan was to have our son spend a night at his Grandparents, he was looking forward to it! so we ignored the smoke situation, and found out while our son was there alone w/ them they were smoking not just in the washroom but right infront of him. We were not very happy about that but didn't say anything and still went for visits as much as we could, we stayed in a hotel the whole time because my Mom said they only have room for our son, which is not true they have a spare bedroom and a livingrom, so anyway the day came for us to head back home, we met my parents at a coffee shop to say goodbye, my son is 4 1/2 and weighs 39 lbs. my Mom wanted me to call every noght we grabbed a hotel to let them know we were all fine, so I did and the last night we needed a hotel I called her and she insinuated that my son was skinny and didn't eat much, which is so not true, after we arrived home a week or so later I recieved a letter in the mail from my Mom, in the letter she told me she thinks my son has an eating problem and I have allowed him to become that way, and said I need to grow a backbone and basically said I was starving my son, she also stated that I didn't care about family beacause we didn't spend much time with them, and to have a nice life!! I wrote her a letter back saying she will not be seeing my son again until he is old enough to make his own decision about you, and we didn't spend much time with them because of the smoking issue, they never smoked around him b4, that we know of but all of the sudden we come to visit and they smoke in the house with their grandson there, I also sent her a copy of my sons BMI sheet with his height and weight from his doctor, proof that he does not have an eating didorder, and have not recieved a phonecall or letter back, so I believe it's safe to assume they have written me off! maybe I was a bit harsh about her not seeing my son again, but I believe that if you are going to accuse somebody of starving their kid, you had better make damn sure thats what is going on! and I am pissed off that she would even think that low of me! all of that was cause by my son not eating a peanutbutter toast while at their house, just because he didn't want the toast she assumes he has an eating problem, I also told her in the letter that I truely think she is losing her mind! There is also another issue I brought up in the letter, about me being sexually assulted as a kid by our neighbour, I told my Mom about that when I was 22 years old, and she told me not to tell my Dad and also made excuses for the neighbour who basically molested me. I said in the letter, what kind of mother does that? and I would never forgive her for that. Anyway.. sorry for writing a novel here but I could use some advice, Would you have felt the same way I did, and did I handle this the right way??? Thanks!