Consumer advise needed

[Red roof]

Hoping someone can help/ advise.
Two years ago I had my solar pv and thermal systems installed. I wanted the thermal system to be able to be hooked up to an ASHP and underfloor heating at a later date when I begin phase 2 of my house renovations, hoping for a simple addition to the existing system. I have recently been informed by the hot water tank manufacturer that the installed tank is not compatible with an ASHP due to the smaller surface area of the heating coil, and that their smallest ASHP compatable tank is 200ltrs, where's mine is 170ltrs. I have been in touch with the installer and been told that someone would be in touch soon. That was about 6 weeks ago and since then I have emailed again and called however they do not respond and they always seem to be in meetings when I call and do not return the call. The company, who I will not name just yet(!), are reputable and even use a photograph of our installation on their website. I am otherwise happy with the pv installation and performance of both systems but I genuinely believe I have been victim to an innocent misrepresentation with regard to the hot water tank. What I would like to know is do I have a case for redress. I don't really want to make veiled threats of legal action that I can't follow through on, and I guess their lawyers would be better than mine! All I would like is for the issue to be addressed and rectified or some sort of compensation for the cost differential. I am located in UK, Scotland to be more precise, can anyone help or advise please?
Thanks for taking the time to read my post, I know it's pretty long!
Garry