During a stock split the only thing that changes is the number of shares outstanding. Typically a stock splits to lower its price per share. Sometimes if a company's value is falling it will do a reverse split where X shares will be exchanged for Y shares. This is typically done to avoid being de-listed from an exchange if the price per share falls below a certain threshold, usually $1. Again the only thing changing is the number of shares outstanding. A 20 for 1 reverse split means for every 20 shares outstanding the shareholder will be granted one new share.
Example X Co. has 1,000,000 shares outstanding for a price of $100 per share. It does a 1 for 10 split. Now there are 10,000,000 shares outstanding for a price of $10 per share.
Example Y Co has 1,000,000 shares outstanding for a price of $1 per share. It does a 10 for 1 reverse split. Now there are 100,000 shares outstanding for a price of $10.
Quickly looking at the news for ASTI it looks like it underwent a 20 for 1 reverse split. You should probably look at your statements and ask your broker how the arithmetic worked in your case.
Investopedia links for Reverse Stock Split and Stock Split