AIBU? Old tenant didn’t change their address

[GinDrinker00]

Lived at my house for 3 years now but constantly get debt letters for the old tenant who lives here. I’ve always returned to sender, however the debt letters still keep coming!
Yesterday my DH opened a letter by mistake addressed to the old tenant and it’s a court summons for council tax for their New property? Would it be unreasonable to phone the council and tell them they haven’t lived here for 3 years and to stop linking our address to them? or would we get into trouble for opening their post by mistake?
I have sent multiple council letters back to the sender for this person in the past but they keep sending them.
I’m worried I’m going to have bailiffs at the door for the old tenants now.

Think some people are disorganised - we get a statement for an account by the previous oweners (we bough over 6 years ago) which has a considerably sum in it! Accidently opened it once when I wasn't paying attention.

After 4 years we got fed up of returning to sender, if they arrive when I have nothing better to do and I can tell who it is ie Blood Donation labled on outside of the envelope, I call to get them stopped.

I keep getting debt letters threatening bailiffs for a gas and electric debt.
The letter is addressed to
X city council
At residential address

I've contacted the agency 3 times and they still arrive

I would. I called the DVLA when three years after they moved we received a SORN notification for their car. For our house. Which doesn’t have off street parking

Hope they got fined the cheeky fuckers.