Why this answer
What actually matters
- Compare the estimate, scope and final invoice.
- Identify extras that were authorised.
- Ask when the need and likely price became known.
- A reasonable price may be implied where none was fixed.
Important nuance
When the statement may have a point
- Unforeseeable necessary work can justify a reasonable increase.
- A clear cost-plus arrangement may permit variable totals.
What you could say
Keep the response tied to the actual rule.
Evidence
What to have beside you
- Quote, order, specification or scope of work
- Messages and call notes showing what was promised
- Photos, reports or other evidence of defective performance
- Terms relied on by the trader and when they were supplied
If they still refuse
Move the dispute forward.
- Define the contractual promise or statutory service standard that you say was not met.
- Ask for the remedy that follows from that problem rather than simply demanding compensation.
- Use formal complaint, ADR or court routes according to the sector and amount involved.
Read the full rules
Go deeper before escalating.
Official sources