The normal flow will be your bank reimburses you from their own pocket. Then goes after the merchant to recover the funds, however if the merchant can present evidence that the charge is valid then the your bank will attempt to claw the money back from you.
Now the important question is here is what is a "valid" payment. Normally the direct debit scheme will outline that that is, and it probably some very simple like there's evidence that you requested the funds are removed from your account. With something like PayPal they can probably claim that the request was valid, at least the bit between PayPal and the bank was, and that the onwards movement of money is a separate issue that doesn't fall under the direct debit guarantee.
It's worth really digging through the small print on these things, they're frequently a lot less helpful than you think, and PayPal has managed to exploit these little holes to their benefit.
Personally I avoid using PayPal where possible and stick to debit/credit card where you have a very simple relationship between you, your bank and the merchant. Which makes disputes much easier, and places the law very much on your side. All this comes from experience dealing with disputes from the banks perspective, and trying to get the right result for the customer, while dealing with payment schemes, and regulatory obligations.
https://www.investopedia.com/articles/personal-finance/05021...
“ But if the item was bought with a debit card, it cannot be reversed unless the merchant is willing to do so. What is more, debit card theft victims do not get their refund until an investigation has been completed. Credit card holders, on the other hand, are not assessed the disputed charges; the amount is usually deducted immediately and restored only if the dispute is withdrawn or settled in the merchant's favor. While some credit and debit card providers offer zero-liability protection to their customers, the law is much more forgiving for credit card holders.”
The business can only dispute if I requested for my money back _after_ the 8 weeks. That's when the evidence and back-and-forth with the business comes in.