From Longman Business Dictionary
telesalestel·e·sales /ˈteliseɪlz/ (also teleselling /ˈteliˌselɪŋ/) noun [uncountableU]MARKETING the practice of telephoning people in order to try to sell them things, or sales made by telephoneSYN TELEPHONE SELLINGour telesales force
Many central heating companies use telesales.