IDM Will provide only unique keys for everyone, So there you may not face any problems while using idm in future.
The answer is very simple and is there in their official website too
IDM have local re-sellers in few countries. Since they are local resellers they will usually support various local payment methods which should be easier to use if you do not have a credit card.
If you are from Pakistan use this Link to see a list of re-sellers in Pakistan.
For other countries you can visit their website and see your local re-sellers.
Important thing is Save your Serial Number that you will get after the purchase because IDM will need it to locate your order if you face any troubles with registration.