was i in the wrong here at work?

ok ill try and keep this as short as possible. i work as a support worker and yesterday i was 5 minutes late. i tried to contact work to let them know i was running late but it kept going to voicemail. so i thought ok whatever ill just sort it out when i get there. i was almost at the clients home when my phone rang. i pulled over and this lady said she would put me on hold because she wasnt sure if the client was going to cancel the service seeing as i was 5 minutes late. so i waited. 15 minutes on hold she comes back to phone apologising saying she forgot she had left me on hold the whole time. she then stated the client wanted to keep the appointment. now im 20 minutes late. i get a call from the big boss today saying dont let it happen again or they will have to document it and it will look really bad and basically gave off the idea id lose my job. its never happenee before. i went on to explain the girl had left me on hold and i wasnt prepared to drive and talk on phone and be pulled over by cops. she said "i get that, but dont let that happen again ok or its gonna be documented" so anyway i asked if shes prepared to put me onto permanent (most get put on permanent after 3 mths ive been there 6 mths) and she said after what had happened me being late she will consider it in 6 weeks. is this fair or what. i feel so screwed over