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I guess it would be better if you tried to log in to the bet105 website with the email you received the bet105 message with to verify if you really opened an account with them, but since you already advised us not to click on the bet105 website link, I believe you wouldn't buy into the idea so that you will not expose yourself to a phishing link. Maybe you opened an account with bet105 and forgot to make use of the account, and that could be the reason they sent you an email with a lucrative offer that would make you fund your bet105 account.
If he said that he hadn't registered any account in said betting platform there before. We are humans and forget about things, but registering in a website you don't remember its name is still uncommon; although who knows, perhaps you're right and it has been so in this case.
Anyway, if it had been me, I wouldn't have clicked on that link either.