Medium overpair spot, I´ll never learn

[Kyer]

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First hand of a GBP 20 (~$40).
1500 starting stack. BB = 20.

Hero limps 8[img]/images/graemlins/diamond.gif[/img]8[img]/images/graemlins/heart.gif[/img] UTG, folds to button who makes it 80, SB folds, BB calls, Hero calls.

Flop: (Pot = 250)
5[img]/images/graemlins/spade.gif[/img] 3[img]/images/graemlins/spade.gif[/img] 3[img]/images/graemlins/club.gif[/img]
BB checks, Hero bets 150, Button minraises to 300

My usual line vs an unknown here is to call and then check-fold the turn, which is ridiculous.

Please help me.