Unhappy client after 25 years of contract with them

I'm a client with MTN from when I was 18 years old. Did not change my telephone number once. A client of 25 years!!!! Now I'm due to an upgrade and suddenly now they change me from a 24 moth upgrade to 36 year upgrade without informing me and let me sign any thing....

Firts when I call they said that I didn't pay my account and legal froze my phone.... the suddenly on no not that they change it to 36 years....

What can I do to get a UPGRADE now and not in 2022