Is it my fault and what would you do or react like as a parent?

Ok so I have been workin in a pre school part time and I began babysitting for a couples only child, 4 years old, it all went well and I worked very hard, playing with the little boy and helping his development just like any professional in child care would do, I made sure he was safe and we had fun, 1 time I read him a story andhe fell aslep in his bed which his parents said was really good4him as they can neva get him2do that. When his parents got bac we wud chat (they wud tel me about their lives)4 sumtimes a gud hour ova my time of bein paid;I didnt mind&1 time I made sum playdough4the child so we cud play with it. Recently ova xmas i have bin very busy,myboyfriends Dad is very ill,I have got a new fultime job wiv NHS,lots of parties&sayn gudbye2 my old job, for the last, I wud say 3 times, I have had2let them down,they wud txt and I wud txt sayin I had plans bcus of bein busy,now they av just txt seemin annoyed&sed 'do we agree that we need a new babysitter'. Am I in da wrong?