Unfortunately, subscriptions made through the Google Play Store cannot be refunded.
If the subscriber can demonstrate that the product (or service) was not usable or available during the subscription period, and the issue was not resolved after trying the troubleshooting steps recommended by Turbo VPN, Turbo VPN may provide the Subscriber with a pro-rata refund of service fees paid at its sole discretion.
Alternatively, please check this Google Play support article about getting a subscription refund from Google Play - https://support.google.com/googleplay/answer/2479637#policy.