Query where to send benefit correspondence to

I am posting to query where to send my occupational pension info to, because on the letter I received from the benefits people, it has included a prepaid window envelope and asked me to make sure that their address is showing in the window when I post it, but, I have tried putting the correspondence in the envelope all ways, and only my address is showing in the window.
The only address on the correspondence is :
St Austell Benefit Centre
Mail handling site A
Wolverhampton,
W98 !1QS

I don't know if the correspondence should go to this address. As mentioned in previous posts, this correspondence is a month past the deadline stated.
The benefits agency told me to send in the form anyway, if I didn't have my figures available at that time, but I forgot, so I put "sorry this is late" on the form.
I intend to send it recorded guaranteed delivery, but I am not sure what address to send it to.
The correspondence I am sending is, their letter asking for my pension info,
The computer generated typed form with my written pension figures in, and:
The actual pension letter showing this years figures from my ex-employer.
I don't want to phone them, as this would be too stressful for me.
My computer has been broken since I last posted on here, and I wanted to check which address to send this correspondence to.
I don't mind putting the correspondence in a plain envelope and writing their address on, I just want to make sure i have the right address, cos I have a feeling it might need to go somewhere else, other than the address I have written above.
Thank you very much, in advance, for your help, I don't know what I would do without this beautiful place to help me.

Yes Chrissy, send it to the address you have.

thank you, i will post it guaranteed delivery and keep receipt.