Compensation for non-returned rental devices

Hi,

I canceled my contract and kept waiting for the instruction on return of the router. I never received any instructions for the return through email or by post. This month I received a bill of 86.25 Euros stating "Compensation for non-returned rental devices". The router has been lying packed in the box for the whole period. How could I return it without the instructions? 

After the bill, while creating this issue, I found the link of "self return portal" on this forum. I already did this process and today I sent the router back.

I request you to return of my deducted money.

Thanks.