How to get in contact with a senior manager/director at Sage to make a complaint ?

After 6 months of trying to resolve a billing issue for a client on Sage Cloud we have been made lots of promises from apparently senior mangers at Sage Stephen Buzzeo being one, for refunds and free periods, absolutely nothing has been done by Sage, they don't respond to emails. The client is completely fed up and wants to go to Small Claims Court to recover their money, but cannot get in touch with anyone in authority.

If someone has had any luck with a complaint contact would be grateful for details