why wont my dad speak to me?

i had a gcse presentation evening on the thursday, and i told him about it weeks before but not the exact time as i wasnt sure what time it was at. anyway, we got letters from school telling us what time it was at on the wednesday. he rung me on the wednesday afternoon when i was at work asking me what time it was at, however as the letter was for my mum she read it not me. i work for my mum, so i went to her office and asked her what time and she said '7pm' as she had read the letter. my mum and dad have issues with each other (i dont know why, they split up when i was really young and they still wont tell me why, but i know it was my dad who did something wrong) and my dad (who is so stubborn) was like 'well your mum could be lying' and stuff.. hes so pathetic. so i was saying 'well why would she lie about what time something is at' because my dad paints this picture like my mum is the devil or something (my mum doesnt have a problem with my dad). so my dad told me to e-mail him the time and where it is and stuff - and i was at work so i couldnt and i was having tea and staying over at my grandmas and she doesnt have a computer so i couldnt of sent him an e-mail, and i had college on the thursday all day. so i explained this to him and i was explaining that she wouldnt lie about the time and he put the phone down on me. he didnt come to my presentation evening, and i havent spoke to him since. this was 3 weeks ago. me and my dad are normally so close and i see him at least 3 times a week, and alternate weekends. what should i do? my mum said i should ring him, but i am a bit stubborn like my dad and dont see why i should as he put the phone down on me and he is the adult. any advice?