Delay in Tier 2 general extension Visa

[Areeny2019]

Hi,
I have applied for Tier 2 visa extension using priority service on 21st of June 2019 ( date of biometric figures collection) . It is not the first time to extend it and i have never had any immigration issues. I have sent a complaint email to HO 18 working days ago and still waiting for a replay and never received an acknowledgment email in return . Also, phoned the contact centre couple of times but nothing happened .
Any ideas what are the possibilities for the delay and what shall i do ? as i want to bring my family over and it seems my children will miss schools .