3 Saying Router not returned

[Samm1]

Three are attempting to say I have not returned the router for my 5g Box, 

I had to ask twice for a grey pre-paid envelope in order to return this item as they failed to send me it the first time but attempted to charge me anyway. They then finally sent me a pre-paid envelope, and so I sent the device off via royal mail (I was provided with a tracking number, however, i have now unfortunately lost that) and so have no direct proof of postage. They are still saying the amount is outstanding, has anyone else experienced this issue? 

[JonathanB]

Hi @Samm1,

Sorry to hear about the delay with your return being acknowledged. When was the router sent back to us? It can potentially take a couple of days for the device to be signed off, so can I double check the timeline with you please?

Thanks,
Jonathan

[Paddiewack]

If you’ve lost your tracking number you won’t be able to retrieve it from Royal Mail so that particular window isn’t open to you. I can only think that customer service MAY be able to liaise with the recipient company maybe using your name ???? However this is very much speculation on my part and as I see it your only option is to go back to customer service or failing that make a complaint via the Three homepage,