You are a project manager and having dispute with your seller over certain changes. The seller claims it's a change request and you think it as a requirement of the product. The seller has formally disputed this. You have met once to discuss the dispute but no agreement could be reached. What should be the best way to resolve this?

A)Take this case to ADR (Alternative Dispute Resolution Team)

B)Continue to negotiate for few meetings and try to resilve the dispute

C) Involve the sponsor to settle this claim