If have received an IOTA payment yesterday and it is still pending.
I've already rebroadcasted the tx two times. Would it be helpful to reattach the tx?
Yes, do the reattach once for an hour. Reattaching works better than rebroadcasting.
Done! Just to get a better understanding. I have now twice the same transaction in the history both having status pending. Will these both be confirmed, but only one counts or will the older one be orphaned and the newer one be confirmed?
Only one will be confirmed. But you don't know which one. The other ones will never get confirmed. Every time when a person makes a confirmed transaction from an address in IOTA, the remaining balance in that address will be automatically moved to a new address in his/her account.