Wifi problems and intrusion errors - HG633 modem

Hello, since Friday 25th November I have a problem with my fibre broadband poster in terms of lots of intrusion warnings and multiple errors on the Wireless side of things. As a result the performance over wi-fi is very poor

 When connected over ethernet, I get no errors and 74mbps download /18.8 upload speed but over wifi , the download speed dropped to 10.6mbps.

My firmware level on the HG633 modem is 1.21t. I'm assuming this has been upgraded recently as I had no issues before 25/11/16. Is it possible to downgrade my modem to a lower firmware level as you have done for the original poster please in this thread please:

https://community.talktalk.co.uk/t5/Superpowered-Fibre-Broadband/also-experiencing-the-disconnects-and-intrusion-warnings-OCE/m-p/1982842#U1982842

If so, please let me know what information you require? Please note, this is urgent as I need to work from home for my job regularly

Thanks

Terry