Did you get the e mail from HO to your personal E mail or Company E mail ?
Did the HO mention any other details in the E mail ?
In which week of April did you apply for visa extension ?
Did HO interview you for the initial application ?
Please see the below link it may be use full for you.
uk-tier-1-entrepreneur-visas/extension- ... 29720.html
according to me,They might dig on how you recruited your employees,how you are getting clients,details of your employees and pay rate,about you profit and loss in the past years.
I found the link @sassybee was talking about.please see the link below
uk-tier-1-entrepreneur-visas/tier-1-ent ... -1800.html
all the very best.See the link i have given and prepare your self everything will be alright
please share your interview experience it will help others.