I created Bitcoin private and public key pair for Bitcoin. I am looking a way to receive funds to my Bitcoin address. The wallet apps which support buying or selling bitcoins are generating bitcoin addresses again. How can I buy bitcoins to my own account instead of wallet generated addresses?
I suppose you are using an HD wallet which all modern wallet apps use, the fact that a new address is created for you each time you want to receive bitcoin is in fact designed to improve privacy and security.
All of the address generated by your wallet which is called an HD wallet are derived from a seed and you are supposed to have a "Mnemonic phrase" (a list of words) which kind of act as your private key and must have been generated at the creation of your wallet.
You can still access the individual private key of each address, keep in mind that exposing them is not secure see @Chris Chen comment the procedure depend on each wallet software, accessing those are usually not necessary.