Hi. My name is*****'m a camera repair technician with almost 30 years in the business and I'll be glad to help you with your question today.
The most likely cause is a broken zoom guide in the lens. This happens sometimes and is usually repairable. However, this is going to require disassembling the lens to troubleshoot and repair by an experienced camera repairman. You may want to check locally for a camera repair shop in your area, or, if you need assistance finding a shop, please let me know and I'll locate one for you. I'll also send you a link to our request line. There's a small fee for this but may save you some time and money.