I have just posted something similar. We are having the same issue. I have written to the complaints team and the adjudications team and only got standard letters back as you describe - that they tried to call (when there are no missed calls and we were in), the complaint is not upheld and we should call customer services.
I have contacted Virgin every month since January about their overcharge. I have had the overpayment back and will check the next bill. I must admit, I only contacted the forum this week and it looks like success. Sasha was prompt and efficient with my issue. Good luck.
Sasha has been very helpful and taken the time to understand and investigate the issues as well as provide a resolution.
Sasha's patience and help have helped restore some of my confidence around VM Customer Services. I doubt if anyone senior reads these things but if they do, I would suggest engaging Sasha to train others in the art of customer service.