Mini splits not keeping house warm?

We just had mini splits installed and our house is COLD! We were told they would handle temperatures down to -5F but even at 40F outside they can’t seem to heat the house higher than 62 degrees. Is this normal? I’m talking about a 1200 sq ft home. We had an assessment of the home and they didn’t recommend additional insulation or window replacement.

Could we be doing something wrong or were we naïve to think we wouldn’t need supplemental heat? Is this a common problem?

Thanks for the advice!