Happens all the time. They sign you up first then do a credit check. I couldn’t get electricity turned on without a huge deposit due (several hundred) to a low credit score.
You get the deposit back after 6 months.
No, this doesn’t happen all the time. They do the credit check up front at the time of application and then let you know that ACCEPTANCE of a contract requires a security deposit. That gives the applicant the chance to accept or decline.