Sons dad

Hi Ladies ,
I’m after some guidance from people who have been in a similar situation . I need help desperately . My son is 4 years old . His dad and I have been separated for 18 months . We were together on and off for 4 years . My son has been seeing a counsellor at a service which specialises in children who have been in family violence situations . I am having councelling at a family violence service . There was coercive control in the relationship I was in with my sons dad . The violence was control and manipulation etc . I’m free now . But my son is not . His dad sees my son for 4 hours weekly . My son absolutely does not want to go he begs for hours for me not to send him . He doesn’t enjoy his time with dad at all . I have a letter from my sons psychologist stating that my son has shown in his play therapy how worried and unsure and scared he feels going to dads . The psychologist has recommended visits to dad he kept to times that feel safe and ok for my son. The letter is 4 pages long and doesn’t paint dad in a good light at all . It recommends he do parenting courses etc .
I’m too scared to give his dad the letter because I’m scared he will retaliate in some way .
My biggest fear is that he will somehow despite the recommendations of the psychologist try to get my son to go to his place more through the court system .
How can I help me son ? Do I give dad the letter ?
I’ve thought things might improve but my son is running away and hiding each time he has to go to dads . My mum does the changeovers due to the trauma I have from the relationship . Either my sons dad or my mum has to physically pick my son up to make him go .
Ive asked my son why he doesn’t want to go, he says ‘ dad has a growl voice ‘.
I have not talked badly of his dad to my son .
How can I help my son feel ok about his visits with dad ? Dad does not make the visits fun - he sits him on an iPad or takes him to run errands .
Please help .