This *really* sucks. As my red-neck dad used to say, don't get mad, get even. This sounds like the sort of situation that makes good press during the slow summer - a potential PR nightmare for the police if they're ignoring a shut and closed case with clear and obvious evidence. Perhaps this will provide the leverage necessary to stimulate some action.
Here are a few things you can do (and that I'll help with if you want):
1. When you speak with or phone the law, immediately ask who you're speaking with and carefully write down the person's name, date, time, and take notes of the conversation - what you asked, and an accurate account of the responses. I've found that asking (and confirming spelling) of the name of the person(s) that answers the phone often has a major impact on the dynamics of the conversation and the likelihood of results (this works in all kinds of situations).
2. After an unsatisfying call(s) or if there's no action in a reasonable time, send a *written* account of the situation, your communications, and the action you want to the appropriate office(s) - this might be Larimer County sherriff, the FC police chief, or both. Dates, times, names, and a brief but accurate account are important. Email is very good for this because it's easily distributed and creates a permanent record. I'd probably say something like "I really want and expect support from the police in this situation, and I look forward to your rapid response. I'm concerned that this is the first in a series of incidents, and if the police are unable or unwilling to follow up on this, I'll have to seek other appropriate avenues to improve or resolve the situation." I wouldn't threaten or demand anything, just make it clear you're not going away. There are multiple crimes and charges in this case - theft, credit card fraud, use of stolen property, etc.
3. Assuming there's still no response, a short, clearly-written letter to the Coloradoan, with a copy to the Larimer commissioners, and the City councils of Ft. Collins and Greeley might generate some action. Politicians love situations where they might actually be able to intervene and help - it's their job and a win-win for you and them.
Since BTO is outside city limits, I'd guess the theft would fall under county juristiction, while the credit card fraud is within city limits. I don't know who prosectues something like credit card fraud (city, county, or state?), but it should be easy to find out. Our county sherrif is an elected official, and the sheriff's elections have been very contentious. I'd think the sheriff's office would want to avoid missing the opportunity to prosecute what appears (at least to us lay public) to be a slam-dunk case and instead get the bad press. But I don't know what the sheriff's office is involved with, and I'd rather have them follow up rapes and armed assaults than car thefts, if they have to choose. What I'd look for is a reasonable response, which you haven't yet received.
If you want help writing, figuring out who to contact, etc, ring me at 970 224-4549 I'll lend a hand.