InterChat Plus is billed through the Apple App Store or Google Play, so refunds are handled by them under their own policies, rather than by InterChat directly.
On iPhone: request a refund at reportaproblem.apple.com.
On Android: request a refund through your Google Play order history.
Where the law gives you a right to a refund, nothing about how InterChat Plus works limits that right.
If you're cancelling rather than asking for money back for a past period, see Cancelling InterChat Plus instead — you'll keep Plus until the end of the period you've already paid for.