Upgrade issue – Towers N' Trolls Review

This game is pretty good but when I spent all my hard earning gems to upgrade the towers, they did not improve at all. The towers are as slow, weak, and short ranging as they were at the beginning of the game. Seeing this made me extremely disappointed because I'm a huge fan of defense games but the game showed no progress in terms of upgrade. Please fix!!!
Review by HassanRocks on Towers N' Trolls.