Hi @Nomibomi and welcome to the Support Forum!
I am very sorry to hear about this. Unfortunately there is no way to change a lock pattern that is already set due to security measures set by Google. There is however two ways to get access to your phone again. Please note though that both ways will erase all personal data from the phone such as photos, contacts, messages etc.
The first option is to perform a software repair in the phone using a computer and our program Xperia Companion, for more information on how to perform a software repair click here. The second option is to use a service called Find My Device. Just log on using your Google-account, find and click on your phone and click the option called Erase.
Try one of these measures and let me know how it went! 
