Only two possibilities:
(a) The people are refunding to some other account; or
(b) They aren't refunding at all.
That having been said, refunds, once issued, can take as long as seven business days to post--although they shouldn't.
In the future, if you purchase using your DEBIT CARD (using it AS a debit card), refunds should be within 48 hours.
Also, check with PayPal (look at your "activity" page) to see that they have actually receive the money. If the "refunds" are going to the proper e-mail address, then PayPal should be reflecting them, after which you can transfer the $ to any account you choose to link.
CONCERN: I am getting conflicting impressions. Are people "refunding" to your bank account, or are they "refunding" to your PayPal account? If the latter, make sure they have the proper e-mail address. Also, PayPal accounts sometimes get deactivated. This can happen from (a) inactivity; (b) suspicious activity; (c) three or more addresses with the same domain (the part after the '@') linked to your PayPal ID--your ACTUAL ID, as in, your name and SSN.