Problem with overstappen

In November 2022 I've signed a contract with you and an option to use transfer service. At the moment my provider was Budget.

Shorty after signing a contract with you I've received message that switching of the provider will happen on 22.02.2023, because my contract with Budget stops then. Also I received a message for contract cancellation by Budget. 

On 22.02.2023 everything was installed by your side, it was working and I have sent back my equipment to Budget.

But my contract with Budget has not stopped. They are saying that they never received a signal from your side that all works and they should stop the service. Also they already charged me for next period.

I've called your support service and I was told that signal from your side is already sent.

I've called Budget support and they say that it is not correct and you yet need to send signal.

Obviously one is wrong and I am having 2 contracts running in the same time and been charged by both sides.

So the bills from Budget will be covered by you now?

I would like a proof that the signal was sent by your side.