How to cancel Solo Mobile plan?

I have been attempting for several months to get this rogue compnay with an imcompetant customer service dpeartment to CLOSE the account. They refuse.
Is there a regulatory body that forces phone companies to actually close an account when a client legitimately pays the bills - owes nothing, - gave them far more than 30 days notice.
The only thing I get is either stuck on hold or " Ok now what did you want me to do then I say close the account"
I ask is it closed now they go ok now say again what did you want me to do?
I say close the account
Again they way No what did you want me to do - Close the account I say
Again they go so let me see now and be clear what did you wnat me to do - I say close the account
Again they go So what exactly do you want me to do - I say close the account.
This game goes on and on and on
'Thye claim the account is still not closed..