Three (UK) complaint letter: broadband, mobile and billing

If you need to make a formal complaint to Three (UK), this page will help you prepare a clear, evidence-based letter. A structured complaint improves the likelihood of resolving billing disputes, network coverage issues, device finance concerns, or early termination fee disagreements.

When to escalate a complaint to Three

Escalate in writing if customer support has not resolved your issue — particularly where the dispute involves poor network coverage, 5G performance below expectation, repeated dropped calls, data speed issues, roaming charges, incorrect billing, device finance problems, or early exit fees. A written complaint creates a formal record and begins the regulated 8-week complaint period under Ofcom rules.

What this letter should achieve

• State your mobile number and account number.
• Confirm whether the issue relates to SIM-only, handset contract, or device finance agreement.
• Explain clearly what has gone wrong (coverage failure, billing error, contract dispute).
• Provide measurable evidence (signal logs, data speed tests, outage dates).
• Quantify the financial impact (charges applied, time without service).
• Request a defined outcome: refund, account correction, penalty-free exit, fee removal, or compensation.
• Request a formal written “Final Response”.

Common Three UK complaint themes (Mobile Telecoms)

• Persistent poor signal or coverage despite coverage map assurances.
• 5G or 4G speeds significantly below expected levels.
• Dropped calls or unreliable data service.
• Roaming or Go Roam charge disputes.
• Early termination fee disagreements.
• Device finance or handset billing disputes.
• Credit file impact linked to disputed balances.

If disputing coverage, reference Three’s coverage checker results at the time of sale and document real-world signal or data speed evidence over multiple days.

Evidence to include

• Your mobile number and account number.
• Contract start date and minimum term.
• Coverage checker result (if available).
• Signal strength logs or repeated speed test results with dates/times.
• Copies of bills showing disputed charges.
• Complaint reference numbers and summaries of prior contact.
• Credit report extract (if disputing credit damage).

Present events chronologically and distinguish clearly between network performance issues and billing disputes.

How to frame your requested outcome

• State the exact refund or credit amount requested.
• If coverage is materially below what was represented, request penalty-free cancellation where appropriate.
• If disputing early termination fees, explain how service standards were not met.
• If roaming charges were applied incorrectly, specify the dates and amounts.
• If your credit file was affected, state the precise correction required.
• Request written confirmation once corrections are applied.

Regulatory timeframes and escalation

Response window: Three has up to 8 weeks to issue a formal Final Response.

If you receive a deadlock letter — or 8 weeks pass without satisfactory resolution — you may escalate to Three’s Alternative Dispute Resolution (ADR) scheme (currently CISAS).

Ofcom regulates mobile providers but does not resolve individual consumer complaints directly.

Practical drafting tips

• Keep the tone structured and factual.
• Use bullet points for dates, speeds, and financial amounts.
• Separate coverage/service issues from billing matters for clarity.
• Retain copies of all correspondence and screenshots.

A concise, evidence-based complaint significantly increases the probability of refund, contract release, or correction in regulated telecom disputes.