I don't really recall if you had the option to disable cache. But it looks clear to me that your problem is:
1. been there since 2001. You probably have a lot more traffic now.
2. More than likely spammers have found your site adding to your page hits.
If you are not willing to upgrade classic to threads or upgrade your host plan. Then you need to tighten your security at your site. One option is to make your board private and moderate registrations. Another is to ban spam IP's. Just for starters.
All of the above is a lot of work on your part.
