How to return back the letter / bills?

Hi,

I've recently moved to Japan and currently staying in Leopalace. There was an Indian staying before on that house and he left to India missing out his Docomo bills.

I'm getting frequent notification to my address on his name to pay the bill and I don't have any contact with him,

There are many letters on his name from Ward office and from NTT docomo.

I'm currently worried that this may affect me ? What I have do on this issue?

I had a similar issue- I took everything to the local post office and explained that I was still getting the former residents' mail and they took care of it and I never got any of his mail again.

Write clearly 「送り主へ返送してください」(return to sender please) on the envelop/post card address side directly and post it.
If you don't write this, the envelop comes back again.
If you receive something via Takuhaibin, do not receive it.
If you received something via Kuroneko-mail-bin, or Hikyaku-mail-bin from Kuroneko-yamato or sagawa transport in your letter box, take it to one of their branch directly and say the recipient is no longer live in the address. JP Post doesn't accept Kuroneko or sagawa deliverlies.

If won't affect you anything if you received someone else's bill of payment. But you must return it.