No invoice provided for work performed

I took my car for a major service at Bosch Selby on the 2nd of June 2015. During the course of that day they called me for extra work they needed to perform which I authorised. When I came to fetch my car they told me they had technical issues so they could not print out an invoice for me but promised to email me the invoice once the issues were sorted out. Up until now and after many phone calls and emails from me to remind them I still have not received my invoice for the work they performed. I am very disappointed by the way they are treating me as I have been a loyal customer to them for years.