I am writing to offer my sincerest apologies for the delay in [action]. I understand that this has caused you inconvenience and I am truly sorry for the disruption to your plans.
I take full responsibility for the delay and can assure you that it was not intentional. I have been dealing with a number of personal issues that have been taking up a lot of my time and energy. I am now starting to get back on track and will be able to focus on my commitments.
I understand that the delay has caused a lot of frustration and I can only imagine how you must be feeling. I am very sorry for any distress that this has caused you and I can assure you that I am doing my best to make up for the lost time.
I will be doing everything I can to ensure that the [action] is completed as soon as possible. I will be keeping you updated on the progress and will do my best to meet the deadlines that have been set.
Once again, I apologize for the delay and any inconvenience that it has caused. I am committed to making sure that this issue is now resolved quickly and efficiently.