As long as you've only created the one wallet - the changing of addresses is normal. Each wallet has multiple addresses that can be used, and the BitPay wallet cycles through them periodically for security purposes.
If it would make you more comfortable, you can update your receiving address in the BitPay dashboard to match the new receiving address in your wallet - to do that please follow these steps:
- Log onto BitPay.com from a web browser
- Click on your name in the upper right-hand corner of the page.
- Select "Settings"
On the Settings page, select "Receiving Addresses" on the left-hand side.