Edit 2: [expletive deleted] Mahdirakib said people from Bangladesh could not use Paypal.
If, according to PayPal, people from Bangladesh are not eligible to use their services, how can you use their services?
Unfortunately Paypal is not available or supported in Bangladesh and you can't use another countries paypal account.
https://www.paypal-community.com/t5/Wallet/Bangladesh/m-p/3063884/highlight/true#M30047Full list of supported countries:
https://www.paypal.com/webapps/mpp/country-worldwideBitcoin is banned in Bangladesh as well. How do you use it, [expletive deleted]?
Unlike PayPal, Bitcoin is a decentralized cryptocurrency.
How are those Bangladeshi Exchanges selling and buying Paypal?
It's difficult to say for certain. Have you personally tried using any of these services? It's possible that these exchanges have registered businesses or private accounts in other countries.
However, all this doesn't really matter since you previously stated that you don't use PayPal. Or did you happen to forget about that?