Euronext CPL8 help?

I have a Euronext CPL8. An engineer fitted this for me and yearly he contacted me and said my alarm needed servicing. He came ever year and ‘serviced’ it with a charge of £85. He also said if I didn’t service it every year then my house insurance would be void. After installation and 4 years worth of servicing it’s cost me £790 in total.
A few months ago the alarm said ‘service due’, a few days later I received a call from the engineer saying it’s time to service. I ignored, then my alarm came up with ‘lock out’. Unusable. I contacted him and he’s saying to come and reset it it will cost £155. This is seriously ridiculous. I own the alarm, I used not be held to ransom and the alarm set to lock out every year unless the engineer comes out and resets the service. He has emailed me the engineers code which lets me in some settings but does not allow the alarm to be set. The instructions says I need a code generating. Where can I get this code generated. It’s 2019 and shouldn’t be like this. It’s a basic alarm, a few sensors and a frigging bell outside. It’s not rocket science!!! Can anyone please help?