1. Open your mail. Just because it looks like junk does not mean it is.
2. Order a copy of your credit report from one on the major credit reporting bureaus. An agency has to "belong" to list your account, so the address and phone number will be able to be found on that.
3. Apply for a bank loan. Request a copy of your pulled credit report. This is cheaper than you ordering it, but worse for your credit rating.