Pro golla in Germany have proved very useful for me. Have bought controller for Panasonic motor from them and will be using them for specific Kalkhoff/Panasonic now 50cycles have all but disowned the bikes. Not surprising given the Impulse motor fiasco.
On my wife's bike I've had trouble with water ingress in the controller (LED one not the later LCD ones) . It dried out, and all I do nowadays is to cover it over with a transparent freezer bag whenever rain threatens. WORKS!!! Hooe your controller dries out or Pro Golla have a replacement.
Also bought direct a walking assist button for a spare bike I bought, which were available in 2008/2010 but hard to find nowadays. The owner (i think) at Pro golla can advise on what's available and you can talk to him on phone, the contact is
https://www.pro-cycling-golla.de/ E
DIT the chaps name is Ulli
Might be worth a try. The site is in german so I've had to resort to Google tanslate at times. Hope you have luck getting going again.
I live in Bournemouth, you'll struggle I think to get any Kalkhoff help locally.
PS Two of our Kalkhoff Panasonic ProConnects are 11 years old this coming August and each covered 17,000+ miles. Still on original batteries. Combined total mileage on all 3 bikes is over 40,000 miles. It's the later/latest incarnations that have the shorter life expectancy I think. You'll see from my sign off, we dabble with a Impulse powered Kalkhoff, but got shot of as soon as the Impulse2 'fiasco' surfaced. Bought some v. Low mileage Pro Connects as back-ups for the future. Bargains at less than £400 and immac low mileage.