The Bitcoin.com wallet simply manages your private keys for you and does not correspond with a "user account" in the typical sense of the word.
If you do not want to use the wallet anymore, you should make sure all funds have been withdrawn, then uninstall the app.
You can also delete just a sub-wallet within your Bitcoin.com Wallet if you no longer have a use for that wallet (for example, a lot of our users delete their BTC wallets because they only want a BCH wallet)
To delete a single sub-wallet, just tap on that wallet from your Bitcoin.com wallet "Home" screen, and then tap on the "settings" cog in the top-right of your screen. Next, select "More Options" and, then, "Delete Wallet" (Please make sure that you read the warning. We cannot help you restore a wallet if you do not have your 12-word backup phrase)
We highly advise that users keep possession of the 12-word recovery phrase for their wallets, just in case you or someone you know accidentally sends bitcoins to one of the wallet addresses. If that happens, the recovery phrase is the only way to ever recover the bitcoins.
If you have purchased bitcoins through the app and created an account then your account would be with a third-party, not with Bitcoin.com.
The services at buy.bitcoin.com and purchase.bitcoin.com are provided by a third-party. If you want to close your account with them you will need to contact their support team.
For buy.bitcoin.com (CEX) please visit: https://support.cex.io/hc/en-us/requests/new
For purchase.bitcoin.com (Simplex) please visit: https://www.simplex.com/submit-a-ticket/