Mail received for ex

I got home from work tonight and there was mail sitting, I really thought it was for me (I need glasses for reading and the lighting was dark) so I picked it up, opened it and realised it was actually for my ex re. a pension fund for a firm he has not worked in for well over ten years or so and he amount is low, but what do I do with it now?  Tear it up and put it in the bin?  Send it back to the firm but not sure he is worth the postage!! 

I keep thinking why now after so many years - I have received mail for him before but realised eventually it was junk but this doesn't seem to be the case here.

Any advice know this is not very important, but at one time it was for me.