After finding out that The Mobile Outlet had gone into receivership, and I hadn't received a single penny of cashback, you can imagine I was disgruntled. I am on a £40 per month 12 month contract with O2 and after consulting this forum, I contacted O2. The Mobile Outlet were supposed to be paying my whole £40 per month back through cashback redemption.
Initially, they didn't really want to know - you'll be aware that they are trying to distance themselves from the scammers, such as Mobile Outlet, etc. But I persevered, and sent a number of complaints - mainly by email - to O2. I pointed out that I believed they should pick up where their 'approved' agents had let me down.
Imagine my surprise when, last Saturday, I got a letter asking me to ring O2 Complaints Service Department [or something similar]. On phoning them, I spoke to a very polite young lady who was sympathetic to my plight. Imagine my further astonishment when she agreed that O2 would put £240 - half my annual monthly contract value - into my O2 account, so effectively slashing my 12 month contract to £20 per month, which is good value given the minutes/texts package I'm on.
Anyone out there in the position I was in [namely, getting little or no cashback from a liquidated broker] take heart. Keep on at your network provider. It can bear fruit

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Richard