Will the phone connect to other sources of Wi-Fi such as coffee shops or another person's home broadband Wi-Fi @mariemc ?
As part of your troubleshooting have you forgotten the network in your phone's settings and re paired up.
Also sometimes it can help if you can split the frequencies in your router to 2.4ghz and 5ghz and then try connecting to one and then the other when setting up the phone.
How to troubleshoot a Galaxy phone not connecting to a Wi-Fi network.
Also try > https://www.samsung.com/uk/support/mobile-devices/how-do-i-clear-the-cache-on-my-device/ You may need to insert your earphones or hook upto a powered On Laptop to access the Clear Partition Section. This may help with lag or stutters as this clears the phone of old/unused or broken cache files.There is also a Repair Apps option in the Menu System too.
I wish you all the best. 
