It isn't a certainty that you'll be promoted. You need to win your league for that to happen. Based on your recent box scores, you are looking up at the 12-0 team in the other division.
You can go one of two ways (in my newbie opinion).
1st, you can stay in a holding pattern, stockpile some money, and buy the best player you can right before the playoffs (probably someone around 30 years old) with the hope that your purchase puts you over the edge.
2nd, you can invest your money in your stadium, and save some money to buy a trainer and a young trainee at the start of next year. At this point in the season you will most likely only be able to obtain a player who as missed out on most of their potential training this year.
I'd go with option #2 -- you probably won't promote this year, but you'll set yourself up in a more sustainable way when you do promote.
Cheers and good luck!