My friend, who also used Betplay and may have at some point connected through the same Wi-Fi
Sorry to hear about your bad experience, OP.
But here's what their terms say about multiple accounts accessing the casino from the same IP (multiple accounts per household):
We may terminate or suspend your account immediately, without prior notice or liability, for any reason whatsoever, including without limitation if you breach these Terms and Conditions.
§ Multiple accounts per household, IP/Subnet or users deemed to be the same person made in order to trick or game Betplay's system in any way are not allowed and will be discarded without warning.
You mentioned that you and your friend might have used the same Wi-Fi network to access the casino. In that case, all you can do is try to prove that you're not the same person (through KYC) and that you weren’t trying to abuse their bonuses or gain an unfair advantage over them.
I believe if you didn’t claim any of their bonuses or play their poker games, that might help your case.