just a question, is it safe to use free VPN services?
No.
"If you're not paying for the product, you are the product."
Some good VPNs offer a free or trial tier, like ProtonVPN, but most (mainly on the play store or chrome extension store) will log your data and sell it for third parties.
also, does VPN uses the same IP address of the country you previously connected before ? or does it change every time you connect to it?
sorry, I rarely use VPN and not that familiar with it.
This varies from VPN to VPN. Must have a pool of IPs which are allocated randomly.