"No response to complaint"

After a very poor experience at Gartnavel eye clinic submitted a written complaint via email to the complaints department. I got an initial receipt of email and have heard nothing since. Tried to call the number for complaints and no reply, tried email again no reply and asked NHSGGC via twitter today how to escalate this and were unable to provide any further contact details. Very disappointed that a complaints department can’t even acknowledge or inform you what’s happening.