Can I re-open criminal and civil cases for fraud after withdrawing them?

I filed criminal charges of fraud against a Dubai resident in 2018 through a UK debt collector. The debt collector told me the criminal case had not been accepted, and so did the defendant. The debt collector may have filed a civil case.

The defendant promised to pay me back and pressured me into withdrawing the civil case. I agreed and signed a waiver to withdraw the civil case. He sent me the waiver to get notarized. I live in the UK.

However, I now suspect that the criminal case may have actually been accepted after all (without my knowing) and that the defendant tricked me into waiving my criminal and civil rights so that the court would be lenient.

What can I do now? I would never have signed the waiver had I known the criminal case had been accepted.

I presume I cannot file the same charges again?

I have evidence in whatsapp chat of him saying there was no criminal case accepted.